Mercenary, known as Youhei in Japanese, is a central character in the anime series 'Zero kara Hajimeru Mahou no Sho'. He is a beastfallen, a rare type of human with animal features, specifically resembling a white tiger. Despite his fearsome appearance, Mercenary possesses a kind heart and a strong sense of justice. His journey begins when he meets the witch Zero, who hires him as her bodyguard. Together, they embark on a quest to retrieve a stolen grimoire that could endanger the world. Throughout the series, Mercenary struggles with societal prejudice while developing a deep bond with Zero.