Kokushibo is unquestionably one of the most dangerous demons in existence second only to Muzan Kibutsuji, the progenitor of demons. During the Sengoku Era, he used to be a Demon Slayer who was driven by his insecurity and jealousy to join the Twelve Kizuki after turning his back on his comrades and his brother, Yoriichi Tsugikuni. Interestingly, he is a member of the rare breed of demons who utilize a Breathing Style against their Nichirin Blade-slinging adversaries.