Austin O'Neil aka The Fifth Ally (Teenage Mutant Ninja Turtles 1990 Film Fanfic)

In the gritty, crime-ridden New York City of 1990, April O'Neil is on the verge of uncovering a mysterious crime wave when she's unexpectedly saved by unseen vigilantes. But April isn't the only one getting a crash course in the city's hidden secrets. Her 14-year-old nephew, Austin O'Neil - a skilled martial artist who has lived with April since his mother's passing in '83 when he was 6 going on 7 - finds himself drawn into his aunt's dangerous investigation. As April's path crosses with the extraordinary Teenage Mutant Ninja Turtles, Austin's own practiced combat skills prove to be an invaluable asset. From the ransacked sewers to the sprawling Foot Clan hideout and the desperate fight on a moonlit rooftop, Austin O'Neil becomes an unexpected, yet essential, "fifth ally," fighting alongside the Heroes in a Half Shell to save Splinter and reclaim the city from the sinister Shredder.