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Izuku liked the way Kacchan’s name fit in his mouth. Liked the way it filled the space, settled between his gums and over his tongue like a full bite of something fluffy and delicious.
He liked how it found its way there naturally, a spontaneous expansion behind his lips simultaneous with the buoyant excitement that filled his chest whenever he saw him.
Kacchan, his subconscious would point out, Kacchan, his heart would cheer, “Kacchan!” his mouth would declare happily, before his brain even caught up to the observation.
It was like the sight of fluffy blonde hair and broad shoulders had its own biological trigger in Izuku’s hindbrain. Just as Izuku blinked and smiled and breathed, did he shape his mouth around Kacchan’s name, letting the lightness filling Izuku at the sight of him spill out over his tongue.
A big whoosh, starting in his gut, squeezing his lungs on its way up, expanding in his chest and tickling on its way up and out of his mouth in a happy exclamation of Izuku’s name for Katsuki.
It would be painful to hold it in. Perhaps that’s why it always came out sounding the slightest bit relieved, because Izuku felt better, always, to let some of that feeling out, vent it the best way he knew how.
And Izuku also loved saying it, his name for Kacchan, a testament to the aged roots of their relationship, his special name, now, since none of their other friends from their young childhood were around.
So Izuku always fit a smile around every Kacchan, because he couldn’t help it, because he loved him so.
And Kacchan always, always looked.
Katsuki couldn’t seem to ignore him if he tried, which worked for Izuku, because even every Kacchan! met with a grunt or a glare or a sneer was at least met, which was more than Izuku could say for the so-called extras.
Without fail, every time, Kacchan’s attention would fall on Izuku if it wasn’t laid there already, and Izuku nearly drowned in the weight of it, however temporary.
And his answering look or scoff or remark was always paired with something content in his eyes, casual, as if it were only natural that Izuku would speak his name as easy as breathing, and that Katsuki would answer.
Even if the answer sometimes only came in the form of looking.
(Secretly, Izuku sometimes thought Kacchan was watching his mouth. But that was, of course, ridiculous.)
(Or so he thought, until the day Kacchan ate his own name right out of Izuku’s mouth, cut him off at the Ka— before the —cchan with his own bite. Scooped it right out like he owned it, which Izuku supposed he did, along with every coherent thought in Izuku’s brain.)