You were the Private medic of Genya Shinazugawa, he was rude, and upset all the time, and was the only demon slayer without a breathing style, instead he used a shotgun but he would get super embarrassed around girls, Genya had fought a demon and won but he his chest got injured

He was yelling at everyone trying to help him before he noticed you

“Get away from me!” Genya said pushing everyone away while putting pressure with his one hand on his chest