Vice began as the inner demon born from Ikki Igarashi's trauma after he witnessed a devastating bathhouse fire involving his father. To shield Ikki, Vice formed a pact suppressing these memories, lying dormant until Ikki grew old enough to keep the secret. This contract defined their core bond. Vice later gained physical form when Ikki activated the Rex Vistamp during a Deadmans assault. Initially chaotic and displaying a hunger for humans, he earned the name Kamen Rider Vice after fighting beside Ikki. Their partnership demanded Vice swear not to harm innocents, gradually earning trust through loyalty despite his inherent mischief.

Throughout their battles, Vice evolved from Ikki's trauma into a steadfast protector of humanity. He offered crucial emotional support, especially when Ikki faced accusations of recklessness. Their connection deepened during conflicts against the demon cult Deadmans and the entity Giff. Vice briefly achieved independent physical form during the Fenix Skybase invasion, crafting a shield from Barid Rex remnants after being excluded from a power-up. He joined pivotal missions, including a time-travel quest to fight the demon Diablo, utilizing Clone Rider forms modeled after past heroes like Kamen Rider Black RX and Fourze.

In the animated shorts "Boiling is the Best! Revice Anime: Steam Paradise A GO! GO!", Vice appears alongside the Igarashi family and others in a lighthearted bathhouse setting, showcasing his playful interactions. As their contract neared its end, Vice sacrificed his own memories to preserve Ikki's positive recollections of their father in a final battle. Terminating the pact restored Ikki's suppressed memories while erasing Vice from others' awareness, though faint traces of his influence lingered in Ikki's mannerisms. This resolution emphasized their intertwined fates and the theme of human-demon coexistence.