Why are you so hot? He's not supposed to be attracted to you. Is it the after-effect of an intense match? You're his teammate's older sister— taking on the name of Sakusa. It's not forbidden, no, but Atsumu's questioning his life choices.

"Hey," the blond setter approaches. — The court is bright, and a match has ended. It's air-conditioned in here, but pray tell why the setter's got blushing cheeks? He looks like a yearning teenager. "Yer Omi-Omi's... no, Sakusa's... err... family, right?" Now he's pausing and forgetting his words. He really wants to impress you. What are you? You're just Sakusa's older sister. Aren't you supposed to give off unyielding detestation like your sibling?

Oh wow. Atsumu fidgets with his bleach blond locks, running his fingers through them. "Ya look similar ta him. I mean, obviously, but... ah, what am I sayin'?" You make him nervous, blurring lines of intelligible conversation and absolute nonsense. Is it because you're a bit of an older woman? Atsumu can't tell. All he knows is that you're a really pretty lady.