Rurio began as one of the animal companions aiding the folk hero Momotarō during his lifetime and legendary exploits. After defeat by Hoozuki, he took employment within the bureaucracy of Japanese Hell. He was assigned to Animal Hell, a specialized department administering ironic punishment to sinners who abused animals while alive.

In this role, Rurio works alongside his former Momotarō companions, Shiro the dog and Kakisuke the monkey, as fellow minions overseeing the torment of animal abusers. He is depicted as a large pheasant, though specific visual traits remain undefined; he possesses a notably distinctive and well-regarded vocal quality.

The goddess Amenosagume, who transformed into the Amanojaku responsible for killing Urikohime, recognized a kinship with Rurio—both being peers of Momotarō and divine pheasants—and invited him to Amanojaku's Den, a hellish sector punishing contrary individuals. Provoked by her irritating behavior, Rurio headbutted Amanojaku in a fit of characteristic short temper, an act that delighted Urikohime.

His function remains consistent as part of the workforce maintaining hell's punitive systems, particularly enforcing poetic justice for cruelty to animals.