Jubei is one of the Six Heroes, Ragna the Bloodedge's master, and Kokonoe's father. He battled the Black Beast alongside Hakumen, and played a part in the Ikaruga Civil War. The Kaka Clan were genetically engineered from his DNA. Despite his physical appearance, he is a powerful warrior, with numerous characters referring to him as the strongest being on the planet. He works to safeguard his friends in their times of need. Before the start of the series, his partner Konoe was murdered by Yūki Terumi. Jubei seems to have an awkward relationship with his daughter, though the reason why is currently unknown.

Alongside his moniker as the strongest being on the planet, Jubei was previously referred to as Mitsuyoshi.