Once a human knight slain by a demon, Tama was reincarnated into the body of an infant S-ranked behemoth monster, though outwardly he resembles an ordinary striped kitten with yellowish fur and brown markings. Severely injured by an earth dragon in a dungeon, he was rescued by the elf adventurer Aria, who nursed him back to health believing him a common cat. Retaining his past life's memories, intelligence, and knightly chivalry, he developed profound loyalty and devotion to Aria, vowing to protect her.

Aria named him Tama when she decided to keep him as her pet and familiar. His personality reflects a noble and honorable disposition, showing strong aversion to those he deems morally corrupt, like his aggressive reaction to nobleman Kasman's harassment of Aria. Despite his noble intentions, physical affection from Aria or other females often flusters him, compounded by her expressed hopes for interspecies breeding once he matures – a prospect complicated by his feline form.

His inherent behemoth nature grants him abilities like absorbing skills and attributes from consumed monsters (slimes, wyverns, minotaurs, golems, poison serpents), augmenting his combat power. He also demonstrates early proficiency in creating a pocket dimension for storage. As he grows stronger through battle and consumption, he gains the ability to transform into a larger, more formidable beastial form. He deliberately maintains the misconception held by most, including Aria, that his powers are traits of an elemental cat, hiding his true identity as a nascent behemoth to avoid being perceived as a threat.

His relationship with Aria forms his core existence; he acts as her guardian and companion, accompanying her on dungeon explorations and intervening against threats from goblin mages to antagonistic humans. He harbors deep gratitude for her saving his life but remains wary of her intense affection and unusual fixation on animals. Beyond Aria, he forms significant bonds, particularly with the blacksmith Vulcan, trusting her deeply enough to allow handling, feeding, armor crafting, and even resting comfortably on her chest. His protective instincts extend to their broader party.

Throughout narrative developments, Tama confronts escalating challenges, including recurring conflicts with antagonists like Kasman and encounters with higher-level demons. These drive his growth in power and emotional complexity, especially concerning the unorthodox romantic feelings directed at him by Aria and others, culminating in open fantasies about intimate relationships despite his non-human form. His journey centers on reconciling his knightly integrity, burgeoning abilities, and unwavering dedication to safeguarding those he cherishes within a perilous world of misconception.