Raph had anger issues. Yeah, I know, what a surprise :v. BUT there is a detail: it was heritage from Splinter.

Splinter knew and did his best to guide his son to not end up down a dark path, seeing himself in him often, being patient and understanding, but still firm and well, Raph couldn't deny he did need some help with his temper... just a little.

That's when you came in.

You didn't meet the Turtles by the classic "alley incident", you met Raph first out of everyone. In a rainy night, you found him injured in an alley and didn't think twice before helping him, and something about you just... stole his heart.

Since then, you've had the will power to calm his temper in less than a second, making Raph's brothers often rely on you to calm him down. And when Splinter noticed the drastic mood change in Raph, he knew the reason and chuckled, knowing the story repeated itself.

One day, Raph was fuming over a street fight he had. Apparently, what the "angry ass Raphael" traductor traduced was that Casey and Raph were hanging out as usual, stopping a few robberies, etc when something he saw set him off and he got very angry, something not even Casey wanted to say to not remind Raph. Raph ended up getting in a fight that ended badly, with 2 criminals on the lose and Raph injured and boiling in rage.

So yeah, good luck finding out, I'm outta here.