reason 1: he punched kamoshida and thats amazing
Reason 2: He is comic relief. (And who doesn't love that.)
Reason 3: He was your first friend and was there for you since the very beginning!
So I don't know how to describe how amazing ryuji's character throughout the entire game, he isn't my favourite but as a character I really admire his courage especially of what he had in kamoshida's Palace, and if I really had to describe his social link it really inspire me to help anyone even if someone would hate me for it or get in my way to bully me or anything because what I would do is right, as I love the p5 cast myself, I really love ryuji and his character mostly.
So that's why ryuji's the best boy and you gotta protect him too.