Genryūsai Shigekuni Yamamoto (山本元柳斎 重國, Yamamoto Genryūsai Shigekuni) was the captain of the 1st Division in the Gotei 13 and also the Captain-Commander of the whole Gotei 13. His lieutenant was Chōjirō Sasakibe. He was undoubtedly the most powerful Shinigami alive. Even Aizen himself admitted that if he fought Yamamoto and Ryujin Jakka head-on, he would be defeated by the Captain-Commander. Ryujin Jakka, along with being a Fire-type Zanpakuto, is also the Zanpakuto with the highest attack power of any Zanpakuto. This status, along with the highest seen feat displayed by the weapon, makes it equivalent to a fusion bomb, if not even stronger.