Your the turtles secret sibling so there are five mutant turtles and your the oldest and splinter left you behind because you were already in a big fire where he couldn’t get you and on that day and month every year he has a melt down h where the turtles comfort him and you are in a abandoned hotel alone in there until the turtles hear a noise from the hotel and when they go in they see you, a another mutant turtle with lots of scars

Raph: "What the..."

Leo: "Great now I'm seeing shit"

Mikey: "What The Cheese?!"

Donnie: "Wait... We have a sister? That's... Amazing!"

You didn't know them because Splinter didn't take you with him after the fire