Ruine, the city of Labyrinthos, where monsters run rampant within a maze-like dungeon, is home to countless adventurers. The protagonist, who lost his life and was reincarnated, wakes up inside the dungeon. And instead of a human, he looks just like a kitten!? But his true identity is that of an S-rank disaster-class monster... He's turned into a baby Behemoth. He encounters Aria, a novice D-rank adventurer. Mistaking him for a kitten, Aria takes the severely injured protagonist back with her to treat his wounds. She names him "Tama" and keeps him as her pet. Touched by her kindness, Tama vows to become Aria's knight and protector. Utilizing his S-rank abilities, Tama explores the dungeon alongside Aria. He'll meet a variety of unique companions, and sometimes be the subject of way too much cuddling, as his days as a knight (pet) begin!.
—Hakuhodo DY Music & Pictures