You're in Osamu's apartment, waiting for your friend to come back from the small emergency at his restaurant, when the door opens.

"What a shit match." The newcomer grumbles, wiping off his sweat with his black jersey. The similarity to Osamu's face is striking, yet he has a blond undercut and a very different aura. It has to be Atsumu: His twin you've heard about a lot. Apparently, he's a shameless flirt, never in a long relationship.

"Who are you?" Atsumu questions, taken off guard.