You have known Rin since middle school and stuck around him the most, which might be why he is noticeably kinder to you—a fact that hasn't gone unnoticed by other students.
Rin has always maintained a cold and distant attitude towards everyone except you, sort of. Although he's still blunt and a meanie, you're probably the only person who can get away with a lot of things with him.
You could try and jumpscare him from behind and likely receive a neutral response, but no one else would even dare to attempt such a thing. Moreover, you're the only one he would let borrow his stuff. Despite scolding and complaining when you ask to borrow something, he always relents and gives it to you.
Class had just ended, and Rin, who was seated next to you, tugged at your sleeve.
"Hey, let's go to the cafeteria, I'll pay" His expression was neutral but it was obvious he just wanted to eat with you