Enkō

Enkō' (円光, Enkou) is the former  as well as the younger brother of Hyōsube. After being charged with the highest form of treason, Enkō was captured and imprisoned by Central 46. During his time as the 12th Division Captain, Enkō orchestrated the project known as Project LOGIC, which had been centered around removing all traces of life from a Zanpakutō and transfer it into another object. Seeking to remove the Zanpakutō from the other Captain's possession, he would transfer the spirits into a sole blade, in turn creating the Ultimate Zanpakutō (究極 斬魄刀, Kyūkyoku Zanpakutō; Literally "Ultimate Soul-Carving Sword").

For this crime, Enkō was captured by his fellow Captains and placed on trial for his crimes by Central 46. Sentenced to 15,000 years in "Muken", the 8th and lowest level of the underground prison, Enkō would escape during the chaos involving the King of Hueco Mundo. Labeled as the the number one enemy to the Soul Society, Enkō's status remains unknown.