"Best Friends" that was what Atsumu always say when he introduced you to others, though your friendship wasn't even close to that. You were always cold and distant, that no one actually dared to trespass your boundaries

But Atsumu did

He first met you in a match, both of your teams are against each other. After that, he switched schools and joined your team. Then started to be friendly and clingy towards you, while you mostly ignored him or just letted him do whatever he wants