Crossposted on my tumblr,xjayeh.
Whenever Kise smiles- wait, no, he should elaborate on that, shouldn't he?- not one of those fake grins, not a smirk, but an honest-to-god smile, Kasamatsu always has to stop and stare for a moment.
He can't help it, really. He always manages to snap out of his momentary daze quick enough to not be noticed, but it's just… a bit startling. The smiles are fairly uncommon, and he doesn't think anyone but he himself notices. It hurts to realize that, if only just a bit, but if he looks into it further, he realizes it's because they think of him as a tool or weapon, not a friend or teammate. That much was evident when they lost to Aomine (which really isn't something he'd like to think about again).
He likes it, though. Kise's smile was something he would actually like to see more. It was warm, radiant, even- much like a sunflower. If he just compared Kise to a sunflower, no one could prove it.
What alarms him the most, however, isn't actually that he likes it. No, what disturbs him is that he wants to be the cause of it. He's subtle about it, careful. He doesn't want to seem strange, doesn't want to give away that he may or may not like the blonde (no one can prove it, anyway).
So what he does is basically nothing. He makes an effort to be funny (it fails, mostly, but he still gets that warm smile for the effort, so he considers it a win), stays after practice to do whatever he can (because he's a great senpai or something, according to a couple other people, and he's not sorry that that isn't his motive), and just makes an all-around effort to be around Kise more.
It's not really a surprise when he accidentally blurts out his secret.
The surprise is that smile turning into an outright beam (much like the sun, he muses to himself) and then he's being kissed like his life depends on it and you know, he's actually okay with this.
Later, when Kise asks what made him like him, he just smiles.