Even before he joins the Mafia, Chuuya is no stranger to pain, he crawls out of the wreckage of the lab worn and hurting, his body covered in bruises and his head thick with fog. Everything aches, but just for that moment he basks in it because it's proof that he's alive.
The next couple years that follow have their fair share of pain as well, it's not always easy for him to find food on the streets and there's many a night he goes to bed with his stomach growling in anguish. He pushes through it though just like he pushes through the pain of the bruises and broken bones he receives, his ability is strong and he's found himself to be much more durable then the other street kids (just more proof he's not human, a voice in his head whispers, bringing with it a different kind of pain), but still there are occasions he knows it's better to just take the hits, to not draw unnecessary attention to himself by using upon his power. In a way, it's the feeling of being weak, of having to be cautious, that hurts more than any of the physical injuries he gets at those times.
After joining the Sheep, the pain in Chuuya's day to day life goes down drastically, there's strength in numbers and with a group of them working together it's easy to obtain the things they need; no longer are there any nights spent hungry or huddled up in a ball trying to stay warm while the wind whips through a too-thin shirt, anything they need they take. He's stronger now too, there's no need for him to retreat from or submit to anyone anymore, he's able to throw caution to the wind, dominating anyone who tries to go against them without gaining so much as a bruise.
Good things don't always last though and when Dazai and the Port Mafia first enter his life they bring with them fresh pain. He's grown used to being in control and so when Dazai's fingers wrap around the back of his neck, snuffing his ability out like one would a candle, he once again feels the old familiar pain of weakness creeping upon him. Being forced to cooperate with the stupid waste of bandages only drives that pain in deeper, but Chuuya's not one to just lie down and suffer, he pushes through and does his best to cause his temporary partner as much frustration as he can in revenge for the pain.
When all is said and done though, none of the hurt he's felt up to the point prepares him for the pain of betrayal. The knife wound in his gut is agonizing, but it doesn't compare to the sheer pain in his heart as those he considered friends glare at him with hostile expressions and speak of killing him.
(It hurts, it hurts so much, but still, he forgives them, it's not their fault)
Joining the mafia brings with it a new set of pains, he's not the only ability user around anymore and for all his skill in fighting he's never had formal training before, more often than not he falls into his bed at night feeling bruised all over from being slammed into the mats. It's a good sort of pain though and he's a quick learner so it's not long before he leaves training with only the pain of tired muscles rather than a beating.
(He can't do anything to train away the pain of Mori's punishments on the few occasions he messes up a mission though, can't use his ability to defend himself from it, all he can do is submit and remind himself that even he didn't have much of a choice, he still chose this life)
Sometimes the pain comes in his dreams too, it's never anything too bad, just the poking sensation of needles and bruising grips on his limbs, but there's always a painful sense of fear accompanying it. He's never quite sure if they're just dreams or memories, never can understand any of the words spoken in them, but he always awakens drenched in sweat and breathing hard.
Those dreams go away mostly after he discovers Corruption, something he would be grateful for if it hadn't brought new troubles with it. With Corruption's awakening pain becomes a never-ending presence in Chuuya's life, the first time he activates it, it feels like he's being ripped to shreds and even after Dazai shuts it off all he can do is collapse on the ground in agony as blood trickles out of his mouth and eyes.
(He's never quite sure if the sound of Dazai crying his name in terror as he falls unconscious is just a pain caused hallucination or if it really happened)
It takes him a week to wake up afterward and several more for the burning pain to disappear, and even then there's a dull ache in his bones that doesn't disappear. He mentions it to Mori once during a checkup, but the man merely hums thoughtfully and tells Chuuya it will most likely fade, before adding that sometimes people need to suffer for the good of the organization.
(It doesn't fade, but Chuuya never brings it up again.)
He desperately wants to never use Corruption again, but Mori's is not one to ignore any tools in his arsenal and so a warehouse is set aside for them to test it in, Dazai always nearby to shut him down before he goes too far out of control. The first time he uses it on a mission is ironically of his own choice, the relationships he builds are of great importance to him and the sight of his dead friends during the Dragon's Head Conflict makes him angry enough to not care about the pain.
His actions net him an executive position and gives birth to the powerhouse duo Double Black, it's an exhilarating prize but at the same time a curse for he's proven the usefulness of Corruption and guaranteed he'll have to use it again.
And use it again he does, though thankfully not as often as he had feared. Whether it's out of consideration to Chuuya, or more likely just out of logic, Dazai always figures it into their plans as only a last resort, it's only under Mori's direct orders that they ever start off with it.
No matter how many times he uses it though, the agony of it never lessens; every time he activates it, while his body carries out its rampage, he remains trapped within his own mind, writhing in agony as his power tears him apart from the inside. It's only when Dazai activates his ability, shutting it down, and he's able to collapse into unconsciousness, that he's granted a reprieve.
Each time he uses it the lingering pain gets worse, no longer is it just a dull ache in his bones but a burning pain in his nerves and chest; he never says a word though, just learns to work through the pain. There's no room for useless people in the mafia and he doesn't want people to think his pain makes him a liability, doesn't want to risk his position. He'll take to the physical pain over the pain of being alone again any day.
(He never even tells Dazai about it, he's come to trust the other boy with his life and loves him like a brother, but he's well aware of how cruel he can be. He doesn't want to risk his mockery or even worse risk being seen as weak.)
When the day comes that Dazai leaves the mafia, it is both a new pain and a relief to Chuuya. On the one hand he was angry, Chuuya was creature of loyalty, even if he hadn't really wanted to join in the first place, the moment he'd become part of the organization he'd devoted himself to it; Dazai didn't get to run away after he'd put so much effort into making Chuuya join, he didn't get to betray the mafia just like he'd made the Sheep betray Chuuya, it wasn't allowed!
(And maybe, just maybe, there's a small part of Chuuya that's hurt he didn't invite Chuuya to come with him, to leave a place where sometimes he felt more like a weapon than a person. He doesn't know how he'd have answered if Dazai had invited him, but he'd thought that maybe Dazai had also considered him family, so the fact that he hadn't cut deep)
On the other hand though, with Dazai gone, Mori couldn't make Chuuya use Corruption, not when no one could stop him. As much as Mori made Chuuya felt like just a weapon at times, Chuuya knew that he had plenty of value outside of Corruption, enough so that Mori wouldn't throw him away as a suicide attack.
With Dazai gone he'd be free of a bunch of pain, he'd no longer have to deal with an annoying waste of bandages, and he'd finally get the chance to make a name for himself outside of Double Black. When he thought of it like that, the situation really wasn't painful at all! And if it took a bottle of expensive wine for him to fully convince himself of that, well, no one but him had to know.
Of course, Dazai had to ruin it by showing up again four years later and pick away at the scabs covering all that pain; still, as annoyed as he was at being outwitted by Dazai yet again, it had been nice to fall back into their old habits of bantering with one another. He remembered Kouyou commenting once not long after they'd first been partnered that they squabbled like a pair of siblings and the horrified looks they had both given her. Truth be told it had made Chuuya kind of happy, he certainly hadn't thought of Dazai as anything like a sibling back then, but it had been nice to interact with someone his own age who didn't fear his ability and would say whatever they wanted right to his face.
Those days were long gone though, the two of them were on different sides now, there would be no more team-ups where they spent just as long attacking each other with insults as they did taking out the enemy instead they would be each other's enemy. Or at least that was what he'd thought but then The Guild had attacked and the weretiger had proposed their organizations form an alliance, and suddenly he was back to fighting side by side with Dazai again, even if it was only for one night.
They had easily slipped back into their old roles, Dazai insulting Chuuya's appearance (and not for the first time in his life Chuuya wished he had a mind-reading ability so he could figure out if Dazai really thought his outfit was bad or if he was just messing with him; then again, Dazai's mind would probably be a terrifying thing to read) and Chuuya would sling back whatever insult he could think of to try and get a rise out of him. He knew he was going to be remembering the slight fear in Dazai voice when he'd threatened to send his address to all the women he'd made cry, for years to come.
Of course, it was just their luck then that one of the Guild members would be conscious and attack them as soon as Chuuya reached the doorway. Once again they switched back into their old roles as Dazai strategized and Chuuya attacked, but none of their attacks had a lasting effect and Chuuya couldn't stop the feeling of dread as he realized what their only remaining option was. Not having to use Corruption even once during the past four years had been wonderful and now, despite what Dazai said about leaving the choice up to him, he really had no choice at all.
Stripping his gloves off, Chuuya approached the creature while chanting rhetoric stanzas that would unleash his ability,
"Oh granters of dark desire, do not wake me again!" As soon as the words were finished pain shot through his whole body, it was likely the pain hadn't increased from the last time he'd used Corruption, but four years without doing so certainly made it feel like it had. Part of him wanted to scream, to beg Dazai to stop him already, but he had no voice with which do so right now even if he wanted to so instead he focused his attention on the fight, trying to ignore the way the tearing pain in his chest and the blood creeping up his throat and seeping from his mouth. It seemed like an eternity before the creature was defeated, one of Chuuya's gravity balls finishing it off after the damage Dazai's bomb had caused, and really why hadn't heard used that earlier, the stupid waste of bandages.
With the creature defeated, he waited for Dazai's touch to end his ability and free him from his mad rampage, but moments passed and nothing happened and all the while his body continues to toss around gravity balls, destroying the landscape around him while the pain his body was in increased. Finally after what seemed like an eternity a familiar hand grasps his wrist.
"The enemy has been eliminated. Take a break now, Chuuya." Dazai's familiar voice washes over him and he collapses bonelessly to his knees, coughing harshly as blood dribbles down his chin onto the ground.
“I told you to stop me as soon as it was over.” He manages to gasp out between coughs, his whole body is an all too familiar mess of pain and he hates it. Out of the corner of his eye, he can see Dazai crouching down next to him, an infuriating grin on his face.
“I was going to, but it was entertaining, so I had to watch.” He comments, his grin never falling and as agonizing as it is to do so, Chuuya turns his head to glare at him,
“I used Corruption because I trusted you.” He growls out, trying hard to hide the hurt in his voice the Dazai’s words had caused; knowing the man as well as he did, it was a 50/50 chance on whether he was joking or serious but that didn’t make the fact he’d let Corruption stay active longer then he needed to any better. He didn’t have the energy to stay angry at his old partner at the moment though, he could already feel his senses beginning to dull as unconsciousness crept in on him.
Raising a fist, he punched Dazai in the chest, though with his current amount of strength it turned into little more than a light tap,
“You... better take me...to the extraction point.” He manages to gasp out before he can’t keep himself upright anymore and tips over, Dazai’s soft assurance that he will, the last thing he hears before blacking out.
(Several hours later when he awakes alone, in pain and in the exact spot he had been, he curses his own foolishness. Curses how he’d let their easy banter and teamwork lull him into thinking that things were somehow back to the way they used to be, he’d let himself forget for just a bit too long that they weren’t partners anymore and that he couldn’t count on him the way he used to. And as he lays there on the ground, still too exhausted to move, he thinks that maybe false hope is the worst pain of all)