Yaku serves as a kunoichi of the Miroku clan, one of only two survivors of a massacre that annihilated their secret village. This attack was executed by the renegade ninja Kamiri and her lover Kugutsumen, leaving Yaku and Miko Mido as sole remnants of their clan.

Yaku bears a unique physiological curse: each full moon triggers her transformation into a powerful, threatening werewolf. This metamorphosis can be prevented only if she reaches orgasm before the change occurs. Failure results in her assuming the monstrous form.

Physically, Yaku has shoulder-length green hair, red eyes, and notably large breasts—traits explicitly noted as a point of envy for Miko Mido.

She continues operating under Miroku traditions alongside Miko, engaging in conflicts against adversaries like the Mahoroba clan, who seek conquest of the Shikima realm.