Lion-sempai, also known as Big-cat, is an anthropomorphic lion employed as a middle manager within a Japanese corporate office. He directly supervises Lizard and Toucan, acting as a relatively kind and patient figure in their work dynamic. Despite his imposing physical presence and predatory species—which often triggers instinctive fear in smaller animals—his gentle personality sharply contrasts with his intimidating appearance. This disconnect fuels frequent misunderstandings: pedestrians might scream "Don't eat me!" during his commute, or colleagues misinterpret his focused work expression as a threat.

He demonstrates notable kindness and tolerance, particularly in managing Toucan's disruptive laziness. Lion encourages Lizard's patience with Toucan, acknowledging flaws while defusing team tension. His home life involves a pride-family; scenes depict him removing lion hair from his business suit with a lint roller before work and consuming meat-based breakfasts. He has a daughter, Shishimura, who participates in activities like making unconventional sushi with her friend Gorimi.

Professionally, Lion navigates typical office challenges, including receiving ambiguous assignments from Company President Turtle and attending mandatory social events like cherry blossom viewings. He experiences work stresses, such as severe tooth pain requiring dental visits—where colleagues attempt but fail to communicate with him. Lion exhibits specific aversions, notably avoiding blood drives despite lacking general disturbance from blood or media violence. He rationalizes this aversion by citing needle sensitivity, though his calm reaction to Lizard's frequently severed and bleeding tail suggests otherwise.

Throughout the series, his character remains consistent: a grounded supervisor balancing workplace absurdity, corporate expectations, and animal instincts. His interactions consistently highlight the contrast between his gentle demeanor and others' perceptions shaped by his species.