Lionel is an anthropomorphic lion demon possessing a tall, muscular physique. His body—arms, torso, legs, and face—is marked by numerous combat scars. He typically dresses simply in brown shorts and black sandals.

Once a bandit lord who terrorized the Demon Kingdom, Lionel's reign ended after the Demon King's fall. The new demon aristocracy, seeking order, contracted Alexander, one of the legendary Four Heroes, to capture him. Alexander, a half-elf, apprehended Lionel and his crew, defeating Lionel in a decisive duel that severely wounded the lion demon's warrior pride.

Sold into slavery as a Demon Capital gladiator, Lionel faced execution in the arena, his masters intending to make an example of him. Scheduled to die against a manticore, he received a final offer: win 10,000 gold coins for freedom. Resigned to his fate, Lionel witnessed a mysterious door materialize in his cell. Passing through it, he entered the Western Restaurant Nekoya. The owner served him despite his inability to pay, providing a pork cutlet rice bowl (katsudon) that became his favorite dish. The nourishing meal revitalized him. Returning to the arena, Lionel defeated the manticore before the crowd.

Determined to secure freedom and settle his growing Nekoya tab, Lionel focused solely on earning the 10,000 gold coins through gladiatorial combat. He achieved this unprecedented feat in under a year. After gaining freedom, Lionel remained in the arena for the next twenty years, defeating every opponent to earn the championship title "The Lion King." Throughout this period, he continued visiting Nekoya to enjoy katsudon, gradually repaying his debt.

Lionel is significantly older than he appears, having frequented Nekoya since the current owner's grandfather ran the establishment decades earlier. His combat abilities are formidable; he fought Alexander to a standstill before losing to the half-elf's superior techniques. He is also a highly skilled swordsman.