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replacement suggestion for people who want the drama of Arahabaki being a voice in Chuuya's head that yearns for destruction and stuff (since canonically it has no thoughts or will of its own and is just raw power):
Picture our Nakahara "I do everything for my friends" Chuuya, Nakahara "with great power comes great responsibility" Chuuya, Nakahara "if I compartimentalize my trauma it can't hurt me" Chuuya.
Picture our guy so raw from using Corruption, or maybe not dealing as well as he thinks with his trauma, or maybe just really tired, or any moment of weakness where you'd want the Arahabaki whispers to kick in.
In those moments of weakness, the Bad Feelings get a hold of him: self-doubt, despair, anger, loneliness. It's so unusual for him to dwell on those things it might as well sound like someone else is feeding him those thoughts. Maybe it adds another layer of frustration. Maybe it does make him want to blow everything up, just to let off some of those feelings.
And maybe in that already bad state of mind, intrusive thoughts enter the field. Things he doesn't really want and things he would never do. Things that make him uncomfortable, things that scare him. He would be able to bring down the Port Mafia. He could kill all those random civilians. He could run away. He already has black holes at the tip of his fingers, he could just destroy everything and leave nothing behind.
And between the very real (but enhanced, put at the forefront) bad feelings and the persistant intrusive thoughts, things might get jumbled in his head. If missing departed friends is real, maybe wanting to get rid of those left is, too. If he's angry at how unfair things have been for him and his loved ones, blowing everything up might be a legitimate reaction. Maybe it really is what he wants? Perhaps that little voice, no matter how scary, is right?
In short: replace "Arahabaki" with "Chuuya's subconscious", for better and for worse. Not to quote Dazai, but: let Chuuya suffer as a human being. Let his struggles be tragically mundane and common.
(and for comfort there's nothing like bringing other people in for a reality check and ground him again)