Cerberus is a small puppy discovered by Kabuto Hanadori. He possesses an oval-shaped face featuring a symmetrical triangular pattern around his mouth, short ears, and a short tail, remaining small enough to be carried. Kabuto initially brought the puppy to school, resulting in temporary confiscation by their homeroom teacher before Kabuto retrieved him. Unable to keep Cerberus in his pet-prohibited residence, Kabuto arranged for Utsugi Tsukimiya to become the primary caretaker, though Utsugi occasionally brings Cerberus to school.

Cerberus shows strong attachment to Kabuto. After a conflict with Utsugi's cat led to him running away, he returned upon encountering Hibiki Kimiya, mistaking Hibiki for Kabuto. While residing primarily with Utsugi, Cerberus has also interacted willingly with Seri Koyuki, who once considered temporary care. Kabuto typically refers to Cerberus as a "sidekick from the past," occasionally calling him an "old rival," and provides the puppy with accessories matching his own.