Youshi, called "The Blue Beast," is a human warrior of the Experts of Justice, marked by her pale-blue skin—a striking feature whose origin, whether natural or artificial, remains unresolved. Married to Taisou, a senior figure within their organization, she combines raw physical prowess and sharp tactical intellect, excelling in combat without relying on supernatural powers. Her signature weapon, a telescoping staff that extends at her command, becomes an extension of her skill in battle.

She proves instrumental in pivotal missions: defending Peking’s Interpol base alongside the mystic Issei against a Big Fire onslaught, repelling attackers but unable to avert heavy losses. In Shanghai, she joins the ill-fated magnetic web operation to disable the Eye of Volger, retreating to the airship Greta Garbo. When the invincible samurai Koenshaku infiltrates the vessel, Youshi assumes command, directing allies to secure the bridge while facing the threat head-on.

Her final act seals her legacy: severing the Greta Garbo’s aft section to trap Koenshaku, sacrificing herself in the process. Her apparent death is later affirmed by the recovery of her shattered staff in the Himalayan wreckage. Her dynamic with Taisou blends mutual respect and camaraderie, punctuated by playful moments like her mock threat to undress after rebuking his unprofessional conduct.

Youshi’s narrative arc underscores loyalty, strategic command, and self-sacrifice. Her demise amplifies the story’s themes of loss and wartime toll, resonating deeply with survivors like Taisou and Tetsugyu. Her portrayal remains confined to the OVA series, with no expanded backstory in supplementary media.