Kirby O'Neil was a devoted parent and a scientist who was kidnapped by the Kraang along with his daughter, April. The Turtles managed to rescue April but the Kraang imprisoned Kirby and brainwashed him. He and April are reunited briefly, but when the Turtles accidentally cause a rain of mutagen ooze, disaster strikes. Trying to protect April, Kirby falls off a building and past some bats; in doing so, he is mutated into Kirby Bat. Nocturnal, he flies above the city in his ghastly new form—but he's still protective of April.