Armorknight Cerberus functions as the primary buddy monster to Rouga Aragami, a key antagonist in Disaster during Season 1. This three-headed canine dons heavy white armor and weaponry, with its center head serving as the dominant voice that speaks collectively. Cerberus exhibits fierce aggression in battle while demonstrating unwavering loyalty to Rouga, frequently expressing concern for his safety during critical moments. Their bond materializes through shared card artwork and flavor text, where Cerberus occasionally teases Rouga about his unusual enjoyment of combat. Cerberus achieves fusion with Rouga's equipment as Armorknight Cerberus "A," embodying their combat unity.

Throughout Season 1, Cerberus remains concealed unless summoned during Rouga's covert missions under the alias "Wolf," aiding Disaster's photon metal collection. It evolves into Armorknight Cerberus "A" during a forced clash against Armorknight Bahamut within Azi Dahaka's specialized arena. Post-evolution, Cerberus participates in Rouga’s battles, including the 5 vs 5 match between Aibo Academy and Sengoku Academy. During Rouga’s duel against Gao Mikado, Cerberus observes Rouga’s battle enthusiasm. Later, during the Gaen Cup, it delivers tactical reminders when internal Disaster conflicts distract Rouga. After Kyoya Gaen expels Rouga from Disaster, Cerberus remains loyal and assists Tasuku and Kiri in destroying the portal generator to Darkness Dragon World.

In later seasons, Cerberus evolves into Tyrant Cerberus, sporting jet-black fur and orange-highlighted armor. During Triple D, this form encounters Bal, rescuing him from Doctor Gara. Grateful, Bal creates the Impact Monster card "Violence Gazer" as tribute. When Gao later requests Rouga’s aid to locate the captured Bal, Cerberus convinces Rouga by invoking their debt to Bal. Tyrant Cerberus retains its signature battle declaration: "I’ll devour anyone who gets in the way! Tyrant Bites!"

Cerberus and Rouga share a bond transcending tactical partnership, reflecting mutual dedication that endures through Rouga’s shifting allegiances and challenges—including his temporary forced villainy under Kyoya’s influence during Triple D. Collaborative cards and fusion mechanics consistently underscore their profound connection across all media.