Genrysai Shigekuni Yamamoto was the captain of the Gotei 13’s 1st Division, the Captain-Commander of the Gotei 13, and the longest-serving captain. Despite his old and frail appearance, he is very muscular and well-defined, and in his prime, was one of the physically strongest shinigami in soul society history.
Yamamoto’s Zanpakutō, Ryūjin Jakka, is the oldest and most powerful fire type in the Soul Society, with more offensive power than any other Zanpakutō. The Bankai is also the most powerful of the Gotei 13 members. When the blade is released, the flames within it burn anything it cuts out of existence, as well as depleting the moisture in an entire area, causing the air and water to dry up. Unohana herself mentions that if used for an extended period inside the Seireitei, its power could easily destroy all of the Gotei 13. Furthermore, Yamamoto’s own body reaches the same temperatures, incinerating enemies who come into contact with him.