Agon never calls Unsui by his name.
He never has. As far back as Unsui can remember, his title on his brother's lips has been an insult, dismissive or mocking or both. He doesn't bother arguing. He knows he will lose, the same way he knew he was doomed to lose years and years ago, when he decided that offering support was better than becoming a forgotten failure of a rival. Unsui will take anything Agon deigns to give him, will offer up any part of himself for his brother's sake. His name is nothing, compared to what he's already committed himself to sacrificing.
There's nothing particularly special about tonight. Agon came into Unsui's room laughing, with the sharp edge of mania to the sound that says it's going to be a rough night, and Unsui didn't fight back when his brother tackled him, just fell back limp and submissive to the bed. That keeps the playfighting gentle enough that it only leaves bruises, and Unsui is more than capable of handling the prints of fingers at his shoulder or against his hip.
Agon drops onto the bed as soon as Unsui falls, still grinning as he shoves the other down and leans in over him. He's straddling Unsui's leg, the press of his weight enough to stop the other from moving, and the long locks of his hair swing down off his shoulders under their own weight, create a curtain around his features.
"You're always so submissive, Unko-chan," he grins, his mouth the same shape as Unsui's but drawn into an expression Unsui's never worn in his life. "Don't you think you could take me on if you tried?"
"No," Unsui says immediately.
Agon laughs, shoves at Unsui's shoulder like he's not already flat on the bed. "Damn right. At least you're smart enough to know that." His thumb digs in against Unsui's collarbone, his fingers flex idly as if he's considering the give of his brother's skin under the push of his hand. "Is there anything you'd stop me doing?" he asks, the words turning rhetorical on his tongue. Unsui doesn't answer - Agon knows the answer to that, has heard it and seen it and made Unsui scream it, sometimes - and the silence is as much answer as it needs to be. It makes Agon grin, draws his grip a little looser so he can drag his fingers sideways and against the curve of Unsui's shoulder to his throat. Unsui doesn't flinch away - this is one of Agon's favorite games, he knows - just lies still, feeling his heartbeat bump against the pressure of Agon's fingertips at his skin.
"Not this," Agon says in echo of Unsui's own thoughts. His hold steadies, the width of his palm digging in against his brother's neck, and he's starting to push, now, pulling Unsui's breathing strained against the weight. "I bet you like this, don't you?" His grin is pulling wider, his weight bearing down further; he brings his second hand in, overlays his thumb against the first, leans in harder. Unsui can't restrain the flinch of hurt at the ache, his body resisting the pressure even if his mind is ever so willing, but he doesn't lift his hands in a futile attempt to push Agon away, just blinks his vision into focus on the clear curve of his brother's smile.
"Not even this?" Agon asks, pushes down hard enough that Unsui couldn't speak if he wanted to. His head tips back in an instinctive bid for air, his inhale scraping audible in his throat, and when Agon laughs it's easy and unfettered. "How far will you go?" He shifts his weight, bears down farther until Unsui's gasps cut off entirely, there's just the frantic motion of his throat against the attempts at air.
"Can you breathe at all, Unko-chan?" Agon purrs. He must be leaning in; he's close enough now that his hair is brushing Unsui's shoulders, catching against the fabric of his shirt. "You can only get air if I let you. You'll let me have your breathing too, huh?"
Unsui can't speak, can't manage a nod. It doesn't matter, anyway, he can't push Agon off and he isn't even trying, defeated by his own knowledge before he makes the effort. His lungs are burning, there's hazy panic starting to wash out over his thoughts; he's pretty sure Agon's never held him down this long, at least not all at once. He doesn't remember this drifting sensation, anyway, the ache in his chest and the buzz in his thoughts like he's detaching from the world, and his vision is starting to blur out as well, fading into white like he's going blind.
Then Unsui is coughing, choking and gasping more air than he can inhale at once, and the hands are gone and there's a voice, panicked and shattered, saying "Aniki, aniki," over and over. It takes him a moment to realize it's addressing him, another to identify that frightened tone as Agon's, and then he processes that time has skipped, that he's rolled over sideways and not on his back and that there's a disconnect in his memories. There's movement, fingers grabbing at his shoulders and shaking him, or maybe it's just that they're trembling so badly Unsui's shaking with it too. He coughs again, gasps air into burning lungs, and when he blinks and looks up Agon is staring at him, his eyes wide and panicked and Unsui can't remember ever seeing him look that way.
"Unsui," he blurts, and all Unsui's blood flashes hot in panic and shock and delight all together at those syllables in that voice. Agon's hands tighten at Unsui's shoulders, grip like he's trying to hold Unsui still or brace himself or both.
"It's okay," Unsui manages. His voice is raw in his throat, it grates over the bruising ache from Agon's hands, but he still sounds better than Agon looks. "It's fine, I'm fine."
Agon stares at him for a moment. His mouth is open on words, or a sob, or maybe just still formed around the sound of Unsui's name. Then he turns away, so fast his hair swings to hide his face, and when he shoves himself away and leaves without speaking Unsui isn't even surprised.
Agon doesn't come back that night.