Kuruyashiki Kenpachi

Kenpachi Kuruyashiki, the seventh generation "Kenpachi," was a Soul Reaper captain of Squad Eleven several centuries ago, contemporary with Kyoraku and Ukitake.

As an exceptionally skilled warrior, he was one of the few to defeat a top-level Hollow during his tenure and declined an invitation from the Zero Division.

With a charisma derived from his forthright and battle-loving personality, and his formidable combat strength living up to the name of "Kenpachi," he earned immense trust not just from Squad Eleven, but from all of Soul Society. He enjoyed duels and observing the end of strong opponents more than anything else.

Later, in a duel with Aizen, he was unable to unleash his full power and was defeated, passing on the title of "Kenpachi" to him. However, he foresaw the emergence of another being like Zaraki Kenpachi and died.

Zanpakuto: "Gagaku Kairo"

A rare biological type Zanpakuto, similar to Uonohana Retsu's "Minazuki."

It summons countless large white spherical creatures, as big as a grizzly bear with giant fangs, that devour enemies.

Although it is a Shikai, its power is so immense that it could be mistaken for a Bankai; he was prohibited from using Bankai for reasons mentioned later.

Release command: "Prosper, slaughter, and emerge; respect the darkness and may the old fade away 'Gagaku Kairo.'"

Bankai: "Gagaku Kairo"

Unusually for a Zanpakuto, the name remains the same as Shikai (though Uonohana’s changes kanji but maintains the same pronunciation).

It manifests an immense "jaw" from the ground, engulfing an area several spiritual miles in radius, absorbing all life and matter, not sparing anything but Kuruyashiki himself. This uncontrollable power devours all, allies and opponents alike, displaying a remarkable capability.

Because of its immense power, its use was banned within the Soul Society by the Central 46, and the backlash from using it renders him unable to even activate Shikai for half a year. His name was revealed by Kyoraku in the novel.