Nearly five centuries ago during the Sengoku Era, Kokushibo was once a human by the name of Michikatsu Tsugikuni and the older twin brother of Yoriichi Tsugikuni. He's the creator and master of the Sword-fighting Breathing Style known as Moon Breathing, which is only matched by his brother's Sun Breathing. Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that compliments his position as Upper Rank One.