Ninju (忍獣 ムキムキねずみ,Ninjuu mukimuki nezumi?) — also referred to as Shino Buff Mice —are intelligent mice that work for Tengen Uzui. They made their first appearance during the Entertainment District Arc.
The mice are specially trained for the purpose of being assistants to Tengen and his acquaintances, as seen during the events at Yoshiwara, Tokyo. They are strong enough to carry one sword per mouse, and are capable of navigating small spaces humans normally wouldn't be able to.