Some TMNT stuff was always meant for grownups.
Michelangelo is the main protagonist of Teenage Mutant Ninja Turtles: The Last Ronin, carrying on after his three brothers had died. He seeks to avenge the murders of his brothers, said to be the work of Oroku Hiroto, the grandson of Oroku Saki.
Michelangelo is the lone survivor of an extermination attempt by current Foot Clan link, Oroku Hiroto, the grandson of Oroku Saki and "bastard" son of Karai. When Michelangelo decides it's time for Hiroto to pay for what he's done, Michelangelo scales the walls to the Foot-controlled New York City and infiltrates the zone. He steals a motorcycle belonging to a young woman called Jones and rides it as far as he can to Hiroto's compound, then crashes it into a tanker truck to create a distraction. While fighting off a cycloptic mouser, he crashes out of the building and is badly injured. Jones shows up and deliberately points the Foot in the wrong direction, following the injuried Michelangelo into the sewer, where he is preparing seppuku. Michelangelo passes out from blood loss, but not before Jones recognizes him as a mutant turtle. He dreams of being back at home with his brothers, but he wakes up in a hospital bed, overseen by April O'Neil.
Mikey finds out that April has been living in the lair with this "Jones" woman, who is actually her and Casey's daughter, Casey Marie. Michelangelo had assumed that April had died in the explosion that killed Casey and Leonardo, but she survived and it literally just cost her an arm and a leg. .