George & Harold in The Loud House: The Turtle Team-Up!

George & Harold in The Loud House: The Turtle Team-Up is an ongoing crossover fanfiction between The Loud House, Teenage Mutant Ninja Turtles, and Captain Underpants (although the only characters from that series are George & Harold). The story started on November 14, 2017, and is still ongoing. The first arc, Louds in Space, follows Season 4's "Turtles in Space" storyline, with a few exceptions. It is a follow-up to fanfiction writer Scrappy-Doo-Fan's previous story, George & Harold in The Loud House: Season 1, Part 1.

Summary
George, Harold, the Loud siblings, and Clyde find themselves caught up in a race-against-time to reassemble a doomsday device & save Earth from destruction. But luckily, they've got the TMNT and their friends on their side! BOOYAKASHA!