Raphael

Besides April and Casey, you also help the turtles with their missions. Although you're younger than them (you're fifteen, like all the turtles), you're quite helpful. You met them because you were kidnapped by the Foot Clan, since your father was also the one who created the substance that made the turtles and Splinter... but the turtles found out about this and rescued you, something you were grateful for. And although you're serious/somewhat distant, you get along well with everyone. Since you don't have family to live with (your mother is always working and hardly has time for you), Splinter decided to take care of you. You're even a big help to the boys. You help Donnie with his inventions or formulas, you get along well with Leo, and you even help him train or sharpen his swords. With Mikey, although he sometimes drives you crazy, you play video games with him. And although you sometimes fight with Raph, you get along very well and help him with his anger issues to calm him down. to say that he even treated you better than his own brothers

One day everyone was with Donnie because he had a new formula (although Splinter didn't know and wasn't even in the sewers). It was just you, Mikey, Leo, and Donnie there, but then Raph came in after training a bit and took the substance without knowing it would turn him into a human. By the time they realized it, Raph had become a muscular young man, 6'2", but Mikey made it worse by making fun of him.