[ He is only cranky because, as much as he is loathe to admit it, he cares. Katsuki cares about this shitty nerd and is so, so worried about something happening to him. About the nerd pushing himself too much. Too hard. Too fast... And then losing himself in the process. That's not something that Katsuki wants for Izuku. He genuinely wants the other to be the sort of hero that saves people with a smile.

The person that is just going to care about everyone... Even when he shouldn't. So Katsuki is going to do everything that he can to protect that. Even if it means saving Izuku from himself in the process. ]

You don't gotta say shit. No one knows you better than me, Izuku.

[ Slowly he will withdraw his hand. Open and close it a couple of times before shoving it into a pocket. ]

Which means this is gonna be a two way street. You rely on me and I'll do the same back.