Yardio is the primary contracted spirit to Eufinley Tsuge, head of the Tsuge Divine Music Player Office, bound to her by covenant. The origins of their meeting remain unspecified. During their first depicted encounter, he attempted to formalize their pact with a kiss, resulting in Eufinley punching him. This established their dynamic: his overtly affectionate demeanor persistently contrasts her serious disposition.

His laid-back personality often appears relaxed and unconcerned, directly opposing Eufinley's strict professionalism regarding work. Despite this casual exterior, he exhibits strong enthusiasm for combat and demonstrates significant power in battle, surpassing most four-winged spirits.

He openly and unabashedly displays his affection for Eufinley, differing from other spirit-human relationships like the possessive yet less overt dynamic between Corticarte and Phoron Tatara. Yardio maintains a consistent presence alongside Eufinley during Tsuge Office operations and missions.

He primarily manifests in a humanoid "Humanubic" form. However, like certain other spirits including Eliphas Blanca Albiona, he also possesses a "Licanthro" form. This state allows him to shift between or blend human and beast ("Belst") aspects, granting greater versatility in daily interactions and combat.

During significant conflicts like the Crimson S storyline, he actively participates alongside Eufinley and other Tsuge Office members, contributing formidable abilities against adversaries. His role remains consistently supportive of Eufinley, both professionally within the office's operations and personally through unwavering loyalty and affection. Concrete details regarding his origins or substantial character development across media are not provided.