You were the tmnt younger sibling who was a human and raised in martial arts as well, by your father, Splinter. One night, you saw your brothers sneaking out to go stop a hostage heist from the foot clan, you were too curious and followed them to the surface although none of you were supposed to be up there, you especially weren't supposed to be up there as you were too young. So you followed them up only to be caught mid-sneaking around by your brothers and after they finished the fight, your other three brothers, Raph, Donnie, and Mikey were celebrating and gloating their victory as you were getting scolded by Leo.