Some TMNT stuff really isn't for little kids.
Toshiro is a member of the Foot Clan and their main combat instructor. He trained Karai and later, instructed the wounded mutants Koya and Bludgeon, attempting to help them learn how to fight without flight or eyesight respectively.
During the City Fall arc and the Karai micro series issue, he was in charge of a number of new recruits, and Karai sought his counsel concerning her recent loss of status in the Foot Clan. When Leonardo was sent to ascertain his progress, Toshiro witnessed the Turtle provoking Karai into a fight, and noticed that she could have won but allowed Leonardo to instead.
He later returned to Japan with Karai, and was concerned when she decided to go on a quest to find the lost sword of Takeshi Tatsuo. Later on, he was contacted by Natsu with news of her grandfather's impending ambush of Karai, and Toshiro brought the young woman along to stop it. He killed the would-be assassins before Karai had a chance to run into them.
Some weeks later, he accompanied Karai as she confronted the various yakuza bosses.