Yomi is one of the Four Emperors, powerful inmates ruling over the population within the privately-owned Tokyo State Prison during a late-1990s era defined by ecological collapse and rising totalitarianism. Under Warden Asano's authority, this faction maintains order among the general inmates. Serving a three-year sentence for a first-offense assault, Yomi immediately opposes Saiga Riki-Oh, a new arrival marked by a six-pointed star on his fist, who challenges the Four Emperors' hierarchy. This antagonism defines Yomi's role within the prison's power structure.