Osorō knew Ayato just because that emotionless guy flirted with him once just to talk with one of his delinquents. His flirting worked on him and his delinquents kept joking about it just to tease Osorō

He sometimes saw the emotionless dude doing favors for someone which is... kinda nice to Osorō. But yet... there's lingering feeling in his heart for Ayato...