Can U Post The Gifs Of Merlin And Arthur Spinning In Transparent Backgrounds Pretty Please

Back on my "Merlin is symbolized by butterflies in the finale, but specifically a species that feeds on corpses because his rebirth and the completion of his character arc are intrinsically tied to Arthur's death" bullshit.

Just for fun, here's a comparison between the purple emperor butterfly (a species that will feed on carrion) and Merlin's butterfly in the finale:

Now, am I reading too far into this? Absolutely. But will the symbolism haunt me for months anyways? Definitely.

So just a typical tuesday

Ok, I don't really post here, but there's a Merlin AU idea that's been rattling around in my skull like it's a pinball machine and I need to get it out, so here we go:

Imagine an AU where Balinor doesn't die and banishes Kilgarrah before sneaking away so Uther doesn't catch him and can't put his newfound son in danger. Of course, both he and Merlin are heartbroken about having to be separated again after just finding each other, but they work out a way to keep in touch and occasionally meet in secret.

And this is all well and good, and everything in the show just kinda proceeds as normal up until about season 4, where we have the knights of the round table well-established in Camelot.

It'd make sense that after a few years of travelling around with Kilgarrah, Balinor would be pretty well-known and well-feared throughout all the five kingdoms as "that dragonlord who escaped the purge and now travels around on the back of a giant dragon", and people all over Albion are kinda terrified of the guy.

Rumors say that he never smiles, that he can kill a man in a split second without even utterring a spell, and can decimate kingdoms with the dragon under his total command. That makes for a formidable figure!

And then one day, Balinor is trying to sneak into Camelot to visit his son (he heard Merlin got hit by a dorocha and wants to make sure he's ok!), and the knights see him and freak out because holy shit that's one of the deadliest guys in Albion!

They're in a tense standoff, with Balinor threatening to call down the dragon on them if they don't let him through. The knights are all ready to give their lives to at least buy the people in the castle time to evacuate, when suddenly Merlin and Arthur make it to the standoff. Arthur immediately starts strategizing with his knights on how they're going to negociate with the sorcerer in an attempt to make sure that they aren't all slaughtered.

Meanwhile, Merlin just laughs and pushes through the rows of knights blocking Balinor's path to the castle. The knights, being very fond of Merlin and not wanting to see their kind little friend be brutally murdered by one of the most terrifying men in exsistence, are trying to grab Merlin and pull him back to safety or shouting at him to get back, but Merlin manages to avoid them as he walks up to Balinor.

For a horrifying moment, the knights and Arthur think that Merlin is about to sacrifice himself for them, but Merlin breaks into a huge grin, yells "Dad!", and runs right into Balinor's arms.

(Merlin and Balinor reason that now that Arthur's king, they might as well start easing him into some of Merlin's less shocking secrets)

And even more shockingly to the knights, Balinor hugs him back, asking Merlin all about how he's been doing, how are his studies under Gaius, etc etc.

And all of the knights just bluescreen. Because the math isn't mathing on this one. Hunith + Balinor = MERLIN?! Does not compute.

They're all pondering how could someone as joyful, friendly, and kind as Merlin be the spawn of a terrifying man like Balinor?? They just cannot comprehend it. The manservant who they all know and love came from this sorcerer who's name is synonymous with the threat of death and destruction??

They're all jolted back to reality however when Balinor asks Merlin if he wants to come back to Balinor's newly-renovated stronghold in the mountains (that's only accessable by riding a dragon) to learn more about one day becoming a dragonlord. And suddenly, the knight understand why Balinor's here. He wants to kidnap Merlin from them and twist him into a terrifying sorcerer to carry on Balinor's legacy!

It all basically dissolves into a long game of high-stakes tug-of-war between Balinor and the knights + Arthur, and Merlin's just enjoying spending time with his father and his friends.

Balinor will just casually crash one of their quests while riding Kilgarrah and "kidnap" Merlin while the knights fight to keep Merlin with them.

Balinor eventually gives Merlin Aithusa so he can get practice raising dragons, and the knights see it as some evil scheme to make Merlin betray Camelot and attack it from within, but damn it Merlin's already adopted the damn thing so now they're stuck with a baby dragon.

IDK if I'd ever write a fic about it since I'm pretty busy writing another fic rn, but I thought that it was a funny idea to throw out there!

PS: if anyone wants to read my current project, where I'm giving Sir Leon more anxiety with each chapter after a kinda-botched magic reveal on Merlin's part (and Merlin may or may not be an eldritch god), feel free to check it out here: https://archiveofourown.org/works/54027337/chapters/136771564

Thank you all for sticking with my incoherent rambling! :D I hope you have a great day/night!

Also, please let me know if you guys wants to hear more of the ideas that pinball around in my head!

Merlin, waking Arthur up one day: Hey, the gods said that it's my turn on the throne.

Arthur, still sleepy: What the hell are you going on about?

Merlin: I'm not really happy about it, but the gods said that their decision is final >:(

Arthur: ???

Gwaine, from the hallway: Are we doing a Merlin coup?! :D

if you ask me, the guy who put the sword INTO the stone should be king, not the chucklefuck who got it out.

And I'm back with Part 3 of the "Merlin accidentally conquers Camelot" au! Thank you all so much for your patience and continued support for this story! It makes me so happy to see people get excited by my silly (and occasionally delusional) au ideas!

NOTE: You can find part 1 here and part 2 here.

EDIT: And you can find part 4 here!

And without further ado, onto the new stuff!

It was rather drafty in the lesser furnished cells of the dungeons. Merlin knew this well, as he had spent many nights during his first couple of years in Camelot trying and failing to get any sleep on the cold stone floors of those cells, kept awake by the freezing chill that would sweep through the dungeons at any given moment.

Merlin also knew that Arthur had never been kept in one of those cells, even on the rare occasions that Uther had him locked up for going against his orders. Whenever Arthur had to be put in the dungeons, he had been put in the fully furnished cells, meant for prisoners who were members of noble families.

Even when they were held in the same dungeon, the nobles and the peasants were subjected to wildly different experiences.

With that in mind, Merlin stopped by Arthur's chambers (or... were they his chambers now? Merlin certainly didn't want to think about that.) to grab Arthur's favorite blanket off of his bed. It was a luxuriously soft blanket, dyed a rich Pendragon red. That blanket was fit for a king and a pain for a manservant to wash, but Merlin had always taken good care of the blanket, knowing how much Arthur liked it.

Merlin folded up the thick blanket with meticulous care, ignoring both his own trembling hands, rendered unsteady by the volatile emotions welling up in him, and Gwaine's presence behind him, silent for once. Despite Gwaine's undying loyalty and penchant for mischief landing Merlin in an even worse situation than before, he seemed to understand the solemnity of Merlin's actions and the profound sense of grief over the life he had lived once before that had been so suddenly torn away from him.

The motions of carefully folding up the blanket filled Merlin with both comforting familiarity and near-crippling sorrow. Would he ever do this again, ever provide support and comfort for Arthur again? As much as Merlin wished to stay optimistic, even if his plan to reinstate Arthur as the rightful king of Camelot succeeded, the darkest corners of his mind hissed that Arthur would never tolerate his presence again, let alone trust him, after usurping him and, in Arthur's eyes, proving everything Uther had ever said about sorcerers to be true.

Merlin's heart plummeted, nearly stopping him in his track towards the dungeon entirely, at the mere thought of what Arthur must think of him now: a treacherous, conniving sorcerer who had manipulated Arthur into becoming his friend only to betray him. Merlin blinked, banishing his tears before they could roll down his face and fall onto the blanket in his arms, and forced his feet to keep moving steadily forward. No matter what Arthur thought of him now, how deeply Merlin has unintentionally wounded his friend, or how catastrophically Merlin's world felt like it was crumbling down around him, he needed to set things right.

Merlin clung desperately to that conviction, the thrumming need to set things right again, as everything else in him wanted to curl up in a dark corner and never move again. After an eternity and yet all too soon, Merlin descended past the gates of the dungeon, where he forbade Gwaine from following him any further, down the noble cell blocks, which were filled with sleeping, but thankfully uninjured knights, and finally through the dark, damp, empty, and cold peasant cells.

He couldn't see Arthur at first, but his magic sensed that he was here. Like always, it jumped, tugging on Merlin to act, whenever Arthur was nearby, causing Merlin to pause his step in order to focus on whatever his magic was attempting to do. This time, it tugged his attention towards the unlit torches lining the walls of the cell block. Light them, his magic seemed to beg of him, our king is cold!

Merlin's immediate reaction was to stop his magic, to push it down so that no one would notice, and, after a deep breath, he did just that. As Merlin stood still, holding Arthur's blanket in his arms and cherishing what would likely be the last few seconds that he could ignore what had happened over the last day and pretend that everything was normal, he heard the voice that he'd been both yearning and dreading to hear for the past day coming from the cell at the very end of the dungeon.

"If you're waiting to sneak up on me, you'll have to try harder than that. I can hear that neither magic nor a crown have made you any more stealthy, Merlin."

Merlin flinched backwards, expecting but yet somehow still unprepared for how much vitriol and bitterness Arthur hissed out his name with. He had heard Arthur yell out his name in variety of tones over the years, ranging from annoyed to bemused to downright furious, but he had never heard his name pass from Arthur's lips like this, spat out from his mouth like it was poisonous and vile. It caused so much hurt to well up in Merlin's chest that he felt it like a bruising punch, causing him to wince in pain, still hiding where Arthur could not see him.

As Merlin stood silently, only a few steps away from Arthur's cell and facing Arthur's well-deserved fury, and tried to desperately blink away the tears gathering in his eyes, his magic abruptly tugged his attention towards the torches again, more insistent this time. Letting out a stuttering breath, Merlin obliged with his magic's request this time, and the torches lining the walls burst into bright, golden flames in an instant, filling the cells with a merry warmth that felt entirely out of place.

Merlin heard a sharp gasp coming from Arthur's cells as soon as the torches lit up by themselves and winced. Right, Arthur was fresh off of Merlin's betrayal, so he was probably pretty jumpy, especially around magic.

Merlin's guilt rose alongside his frustration. Everything he does with his magic, he does it for Arthur, and yet every single damned time it backfires on him and somehow hurt Arthur! A spell meant to heal his father kills the king instead. A battle waged to ensure his continued reign steals his sovereignty instead. And lit torches meant to provide him with warmth and comfort scares him instead!

But before even more guilt could build up inside of him, Merlin heard Arthur's voice once more.

"I won't be scared by a coward of a sorcerer who would steal everything from the man he claimed to serve! Or is the great Emrys too important to even face the fool he tricked into believing that he was his friend?"

Before Merlin's mind could even process Arthur's words, his feet were already carrying him to the end of the hallway, right to the front of Arthur's cell. He needed to prove Arthur wrong here, their years of friendship weren't a lie or a trick, Arthur needed to believe that! Too much of Merlin's life, his very soul, was woven into his bond with Arthur, he couldn't let Arthur have any doubt that their bond was even real!

As he finally arrived at the door to the cell that held Arthur, Merlin's heart stuttered again, this time with grief. Based on the ferocity in his voice, Merlin had expected to see Arthur pressed up against the bars, ready to battle his perceived opponent. Instead, he was greeted by the sight of Arthur, sitting alone on the dirty stone floor, his face wearing the same dejected and defeated look it had just days earlier, after Morgana had taken the citadel and Arthur doubted his own ability to rule his people. The only difference was that the lost look in Arthur's eyes from before was gone, replaced by a scornful glare that had Merlin feeling like he was the scum of the earth.

Merlin opened his mouth, ready to apologize, plead for forgiveness, whatever it took to just stop Arthur from looking at him like that, like Merlin was his enemy, but no words could form in his mouth, as too many emotions were welling up in his chest that it closed off his throat entirely. Merlin drew in a deep, fortifying breath, purposefully avoiding eye contact with a still-glaring Arthur the entire time. Once he felt like he had his feelings even marginally under some tenuous control, he finally met Arthur's gaze and held out the blanket like a pathetic peace offering.

"I brought you your blanket. I know it gets cold down here."

Merlin was rather proud that his voice only wavered slightly, not giving an indication of how disastrously close he was to breaking down into tears in the middle of the dungeons. Arthur merely stared at him for a moment, bewilderment appearing on his face for a few seconds before it was quickly wiped away by angry sneer.

"I don't accept gifts from the likes of you, sorcerer! It's probably cursed or enchanted to kill me so that you can finally get me out of your way for good!"

"No!"

The blanket fell to the floor as Merlin grasped the bars of the cell with both hands and pulled himself as close as he could to Arthur, who had flinched back at Merlin's outburst. His magic flared again, wanting to break down this barrier between them so that he could get closer to Arthur, but he denied its request, knowing that such an action would only agitate Arthur even more.

"Arthur, please, I never meant for any of this to happen! You must believe me! I only wanted to for Camelot to be safe from Morgana and for you to retake the throne! I only want to secure your reign, not end it!"

That, it seemed, finally got a reaction out of Arthur, but it wasn't the one Merlin was hoping for. Arthur finally stood up from the floor and stormed over to the cell door, getting close to Merlin, but just out of reach.

"And why on earth should I trust a word you say?! You've done nothing but lie to me for years, even when I gave you my complete trust! I thought you were my closest friend, the one person in my life who would never betray me, but as it turns out, I never even knew your real name, much less where your true loyalties lie!"

Merlin's face fell at Arthur's accusations, knowing that he was, in some ways, completely right in them. Still, he met Arthur's accusing glare with as much honesty as he could. After all that his own actions had taken from Arthur, he owed him the truth at the very least. Merlin spoke again, trying to muster up a calm, soothing tone despite his strong emotions.

"I know that you don't have much reason to trust what I say now, but I will do all that I can take make this right. I was born with magic, yes, but I was born this way for a purpose, and that purpose is you, Arthur. I am Emrys, destined to be the guardian of the Once and Future King, who will rule over the greatest kingdom history has ever known and bring peace the likes of which has never been seen throughout the land."

Merlin could see the moment of realization on Arthur's face as he put together who exactly the Once and Future King was, his eyes going wide with shock. Despite the situation, Merlin has just a bit of a smile on his face as he reminisced on fond memories.

"When I first met you, I just couldn't understand how such a prattish clotpole could ever be a king of legend, but the longer I stayed by your side, the more I could see the king that you were destined to become. A great man, a great leader, who will always stand up to protect his people, even if it means putting himself in danger."

Merlin's speech trailed off as he smiled gently at Arthur, trying desperately to give him reason to believe Merlin, to believe in the prophecy that tied them together, and, above all, to believe in himself.

To Merlin's surprise, he could see Arthur confusion melting into... something. It looked like something along the lines of hope or awe, which gave Merlin hope in return. But just as quickly as it was there, Arthur's expression shifted again to a frustrated anger.

"Even if what you're saying isn't some trick, your little bedtime story is wrong anyways! I can't be the Once and Future King if I'm not even a king in the first place!"

Merlin sighed deeply, knowing that they'd get to this point eventually. He had a plan, but would Arthur ever agree to it?

"I've tried! I tried to simply order the council to make you king again, but they won't do it! Geoffrey stopped me with some old laws that Bruta wrote! He said that I can't abdicate the throne to you because you're no longer legally a nobleman."

Arthur eyes widened frantically at the mention of Bruta's laws, his breathing picking up with panic. He backed up from the bars of the cell and began pacing around.

"Bruta's code, damn it, I forgot that they applied in these situations! Wait..."

His eyes snapped back to Merlin, looking red-rimmed and on the verge of tears. His voice, which was so full of fire mere seconds ago, now sounded hollow. Merlin's hope wilted upon seeing Arthur like this, and his magic flared again, still wanting to destroy the barrier between them.

"This means that the Pendragon house is no longer recognized, doesn't it?"

Merlin could only nod, unsure of what he could do to comfort Arthur. At Merlin's confirmation, Arthur took a shaky breath, trying to collect himself from the inner turmoil that he was surely experiencing.

"Everything... I've lost everything."

Merlin gave Arthur what he hoped was his most comforting smile, but it didn't do much for Arthur's hopeless disposition. After a small sigh, Merlin spoke again in a soft, comforting voice.

"Arthur, all is not lost. I have a way to make you king again! We just have to make you a noble again, and then I can abdicate the throne to you! And luckily for both of us, there's an easy way to make a peasant a nobleman quickly! And you should know, you wrote it into the laws yourself!"

Arthur blinked at him, not comprehending what Merlin had said for a couple seconds, before a sliver of hope showed on his face. However, as soon as it was there, it was gone again, once more replaced by anger and betrayal. Arthur quickly stormed over to the cell door, this time reaching the door itself and wrapping his hands around the bars so that he could yell in Merlin's face.

"I knew it! This was a trick!"

"What are you talking about? How would me knighting you and then giving you back your throne be a trick?!"

"You would have me swear on oath of fealty to you, which would legally, and for all I know magically, put me under your command! This was all just another plot to control me, wasn't it?!"

"Oh come on, you wouldn't have to mean it when you take the oath! You'd just have to say the words and then let me abdicate!"

"So now sacred oaths of loyalty are nothing but empty words to you?!"

"Gods, you really can't make anything easy for the both of us, can you, you prat! I'm just trying to give you your crown back!"

"You would have me disrespect the sacred oaths of knighthood! I would never swear an oath of fealty to you! It is a sacred bond of trust, which is apparently something that you know nothing about, Emrys!"

Merlin flinched back, still unused to Arthur saying the name given to him by the druids, much less hissed out in anger. Merlin backed away from the cell door and took a deep breath, trying to find some solution to this mess.

"So, I take it that you would not accept a knighthood from me?"

"Never."

Merlin sighed again, his eyes drifting around the dungeons as he tried to think of a different way to make Arthur a nobleman. Eventually, his eyes drifted back towards Arthur, who was still holding onto the bars of the cell door. As Merlin looked at Arthur, pondering any solution that he could possibly come up with, a metallic flash caught Merlin's eye, drawing it to Arthur's left hand.

There, the torchlight was reflecting off of Ygraine's ring, the one that Arthur rarely ever took off. Merlin was glad that Arthur still had it with him after everything that had just happened to provide some comfort, but it still didn't present Merlin with any solutions...

Wait.

Oh no.

Swallowing thickly, Merlin called out to Arthur again.

"Arthur, do you know of any, any other ways to elevate a peasant to the status of a noble?"

"I'm afraid not. Me granting knighthoods to peasants was the first legal opportunity for peasants to elevate their stations. There is no other way."

Merlin closed his eyes and tried to hold back his frustration. He wouldn't have to resort to that, surely?

"And you've really thought this through, Arthur? If you don't accept a knighthood, I don't think that there's any other way that I can legally make you a noble again, much less the king. Are you really prepared to go the rest of your life as a peasant with no title, no lands, no riches, nothing?"

Merlin could see that his words gave Arthur pause, forcing him to at least reconsider Merlin's offer. Merlin internally pleaded with Arthur to please don't be an idiot, just take the offer!

Finally, Arthur seemed to have reached his decision, as he glared at Merlin once again with conviction.

"I might be forced to live out my days as a peasant, but at least I'll be a peasant with my honor and integrity intact."

Merlin was, at this point, sorely tempted to bash his head into the stone wall behind him. Why, why did this clotpole have to make his life so difficult?!

Merlin gave a heavy sigh as he nodded, accepting Arthur's decision. Arthur looked rather smug about Merlin conceding to him, which he wouldn't be feeling if he knew exactly what Merlin had in mind as his contingency plan.

"Very well then. You've made it clear that you won't willingly take this one opportunity for me to give you your throne back. But make no mistake, you are the Once and Future King. This is your destiny, and I will see that it comes to pass, no matter what I have to do. I know that it might be unfair, but I only ask that you forgive me for what I do next. Please remember, everything I do, I do for you and the kingdom that you're destined to build."

Arthur's expression had gone from smug to confused to concerned very quickly, but Merlin didn't acknowledge the slight fear that had appeared on Arthur's face. Instead, he carefully pushed Arthur's blanket, which had been lying at the foot of the cell door, through the bars, ensuring that Arthur could grab it.

After that, Merlin turned on his heel and walked out of the now silent dungeons, his footsteps sounding authoritative and ominous as they echoed off of the stone walls.

Despite his measured footsteps, Merlin's mind was moving at sprinter's pace, trying to plan out everything that would need to be done in the coming days. The first thing that he definitely needed to do was let the steward know that he needed to plan a wedding on short notice.

After all, it wasn't uncommon for conquerors to marry their war prizes.

I hope you all enjoyed this continuation! Were you right in your guess as to what Merlin had in mind at the end of part 2? Please let me know if you'd like another part of this story!

I'll try to tag everyone who asked for a part 3 here. Thank you all for your support!

@magic-mushroomss @miyriu @whole-buncha-snakess @achillesuwu @aerismoon

@tidalwavesandthunderstorms @marki9 @isaidno @retro-wallflower @samwinjester

@lascienzadellafantasia @sugar-coated-prat-dragon @theoldfroglady @ryeallytired @mind-of-a-crow

@whynotreinventmyselfeveryday @likeapaperplane @odinjm @orliththedragon @aglmry

@caraspud @aostrek-236 @justaz @slippysalt @coffee-shop-gay

@the-king-and-the-druidess @theroundbartable @fanfic-library-for-me @linotheghost @scuttlingsleipnir

@guiltyscarlet

And, as always, than you for reading through my ramblings! :D

I got tagged, so let's do this!

That was fun! I feel like this description is very fitting with my username. I approve! >:D

Thanks for tagging me @rainbowsmagicandshit!

Saw this going around twitter, looked like fun. What? I'm not procrastinating (I am, I really am)

Make this picrew of yourself

Take this uquiz

Post the results side-by-side. No pressure tags: @alypink, @revnah1406, @madefordvarka, @deadbranch, @welldonekhushi, @kaitaiga, @applbottmjeens, @froglights-and-pearls

the absolutely LETHAL face card that is s5 merlin… bamf!merlin truthers rise!

I'd definitely watch that, but I would want to know if the writers would give Uther a weird amount of sexual tension with young Gaius (or maybe young Balinor). Because there was SOME past there, and I'm honestly kinda scared to find out lol!

Prequel idea:

In a land of chaos and a time of dragons, the fate of a great Kingdom, rests on the shoulders of a young man. His name?

Uther

(a series in five seasons)

Waiting 20 long years (probably like an hour) for my devoted husband (ao3) to return home from the Trojan war (being down) and slay my horrid suitors (error message screens).

Series 1 Trailer for @larluce's awesome Time Travel AU!

Merlin's arms strain with the effort of hauling Arthur, barely-conscious, towards the misty shores of Avalon. It takes little more than his presence to call the Sidhe forth from their sanctuary in the lake, but Arthur groans with both pain and shock as their winged blue forms fly out of the water.

"You must save him! I am willing to give up my own life, but he must live!"

Arthur weakly struggled in Merlin's supportive arms, protesting Merlin's plan now that it had become clear that Merlin was set on self-sacrifice.

Hovering above the gleaming surface if the lake, one Sidhe gave Merlin a sharp, almost menacing, grin.

"While we cannot take your life to exchange for his, Emrys, there is another sacrifice you can make that would save your king."

------------------------------------------------------------------------------

Arthur gently places a young tree that's barely tall enough to brush against his knees into a prepared spot in the center of the royal gardens.

There are no tears on his face, for he ran out of those long ago.

"I hope you like the view from here, Merlin. I think you'll be able to see out over all of Camelot in a couple years."

------------------------------------------------------------------------------

The knights watched as Arthur viciously pulls out the axes that had been stuck in the tree's trunk and had carved a large gouge in its base. Arthur whirled around at them, and many, including his closest companions on the round table, flinched back at his near-feral expression.

Arthur's eyes locked into the spy responsible for this.

"Anyone who so much as touches this tree pays for their transgression with their head."

------------------------------------------------------------------------------

"So you can perform the spell, then?"

"We can, your majesty, but only with the proper materials. A blade bearing the lifeblood of 300 men and 3 dragon scales are not easy to come by."

Arthur leans forward from where he's sitting on his throne, his eyes wild in a way that disturbingly reminds the druid delegation of the look in Uther Pendragon's eyes as he hunted down every living creature with a hint of magic.

"Do not concern yourselves with that. I will gather these materials for you. Just make sure that you can perform the ritual successfully when the time comes."

------------------------------------------------------------------------------

Two pairs of eyes, the owners of which both believed themselves to be dead moments before, blink open to the same sunny morning. An unforgettable morning that they had both lived through before, many years prior.

This was, after all, the morning that their destiny was set into motion.

------------------------------------------------------------------------------

I hope you enjoyed this! I tried to write some scenes that are implied in larluce's au, but are never directly shown, so that you aren't spoiled for many scenes in the au!

Check out the time travel au here! (You should definitely go read it right now because it's awesome!!)

This idea is so dear to me! Because we see Arthur self-loathing so many times, both in relation to himself and his father's legacy, but it goes further beyond that.

There's a deleted scene from either "The Tears of Uther Pendragon" part one or two where Arthur is discussing Uther's descent into madness with Merlin. Arthur reveal's that Uther's father fell into a similar state later on in life, and Merlin "helpfully" points out that he learned from Gaius that those sorts of things tend to run in families. This leads to Arthur glaring at Merlin in anger at the accidental implication that Arthur himself would fall into a similar state of madness one day.

So, we can make a logical guess that Arthur, on some level, believes Pendragon blood to be cursed with madness and bloodlust. While it doesn't really come up again later in the series, we can assume that Morgana being revealed as Arthur's sister and becoming a tyrant only further solidifies this belief in Arthur.

To Arthur, he killed his own mother with his birth, having been born a murderer and trained form that day on to be the perfect warrior. To Arthur, he is damned by his own loyalty to slaughter as many people as it takes in the name of protecting his kingdom, and he's never known a single day in his life without blood on his hands.

And, on top of all of that, madness and tyranny runs through his blood, as evident from his father and half sister.

Arthur wants so very badly to be a good king, to be kind and protect his people, but he feels like he can never achieve that with all the lives he's taken and the evil that runs through his own blood. He could not carve out the part of himself he sees as rotten more than he could empty his own veins.

That's part of why Arthur is always so awed at Merlin's never-ending loyalty and kindness towards Arthur. Arthur sees himself as good for nothing except violence, and he does not know what to do with Merlin's soft care.

“something is rotten inside of me, i have to find it and cut it out” — house song; searows