During the fight between the 1980s, 2000s, and Original Turtles versus Utrom Shredder in the source world of all Ninja Turtles (the comics), more than just the turtles, Shredder(s), and Technodrome were brought into what Shredder calls Turtle Prime
When the fight first started, a girl who had been planning on joining the Shredder's army was trapped on the Technodrome and taken into Turtle Prime with everyone else. Unfortunately, she got scared and decided to run. Only when she left the Technodrome she found a much different world outside it's doors than what she is used to. Instead of the bright lights of New York City with all it's people, noise, and cars...she finds a dark, quiet, and gritty place.
It's the strangest place she'd ever seen. Not only does the whole city just seem so different environmentally, but it physically looks different. It's all black, white, and gray. There are no colors. The sky is completely clouded for miles and miles around. All the buildings look old and broken. And the lack of people around is strangely scary.
It's her bright colored hair and clothing that attracts attention of this dimension's Shredder. He attacks her, meaning to kill, and the Source Turtles save her. But since the other turtles and the Technodrome are gone now, they have no way to get her back to her dimension. At first she seeks to join the Shredder of this world, but quickly finds out that this Shredder is not as easy to get involved with (business wise, not romantically) than the one she is used to. In order to survive, she must join with the Source Turtles (who are much different from the ones she is used to dealing with). They, however, are not as easy into trusting either.
***Girl can be a guy.