Gembu is a special attack utilized by the Ninja Turtles in Teenage Mutant Ninja Turtles (2003 game). It gathers together all four brothers (summoning any that aren't already present), and unleashes pure Turtle fury.
The attack is named after Xuanwu (玄武), a Chinese tortoise deity known as Genbu in Japanese. Genbu is often characterized as a two-headed tortoise, or a tortoise with a snake wrapped around it. The latter is depicted in imagery on the screen when the attack is used.