The naive younger brother, called the "Fanged Ninja". He originally resented Ikazuchi for staying in the shadows for 500 years, idolizing his brother and respecting most of his decisions. But Isshuu took the fact they weren't rebuilding their Ninja school personally until he found the resting place of his father's sword, Kiraimaru. Desiring to rebuild the Ikazuchi School, Isshuu used the blade with disastrous results. But after learning to use the Kiraimaru in a way where his friends wouldn't be harmed, Isshuu decided to rebuild the school after Universal Stealth Group Jakanja was defeated. He was later shown to have feelings for Nanami Nono.