Michio Kaga hails from modern-day Japan, scarred by severe bullying that included physical abuse in elementary school and social ostracization during high school. His home life descended into neglect and abuse, worsening significantly after his mother's death under his father's intensified mistreatment. This profound trauma drove him to contemplate suicide. During this despair, he discovered an online portal disguised as a fantasy game character creator. After meticulously optimizing his character and achieving a high bonus roll of 99, he accepted the terms without fully grasping their irreversible nature, resulting in his transportation to a fantasy world.

Physically, Michio appears as a young man with purplish-black hair and eyes, frequently shown wearing a jersey. Subtle tufts in his hairstyle resemble devil horns, hinting at his cunning nature. Animated adaptations shift his hair and eye color to black, differing from the blue hues in original illustrations.

Initially melancholic and distrustful due to his past, Michio adopts a pragmatic and cautious outlook upon realizing his new reality is permanent. Survival becomes his paramount focus, compelling him to meticulously analyze every risk and opportunity. He leverages his unique "cheat" abilities—Appraisal (assessing strengths/weaknesses), Character Reset (reallocating jobs/skills), and Equivalent Exchange—to navigate this world. Combat skills rooted in kendo and aikido training are tempered by his avoidance of unnecessary fights; he prioritizes safety through repetitive labyrinth exploration and strategic retreats. A critical limitation is his "Mana Sacrifice" ability: depleting MP for powerful attacks triggers severe depression and cowardice when his mana runs low.

His personality blends analytical logic with protective loyalty. Though initially uneasy about slavery ethics, he purchases the wolfkin Roxanne as his first slave, treating her as an equal partner. Their relationship evolves into romance, establishing a pattern where he acquires additional slaves—Sherry (dwarf), Miria (catkin), Vesta (dragonkin), and Rutina (elf)—forming a harem. He ensures their well-being with high-quality food, equipment, and autonomy in clothing choices, starkly contrasting typical slave treatment. Despite a marked libido amplified by his "Sex Maniac" job, he emphasizes consent during intimacy and avoids forcing discomfort. He reacts with lethal aggression to threats against his harem, displaying intense possessiveness, yet conceals abilities like teleportation to prevent geopolitical misuse.

Character development charts his adaptation and emotional growth. Early naivety yields to shrewdness, evidenced in bounty hunting and resource management. Relationships deepen through mutual respect: Roxanne becomes his trusted confidante, Sherry's intellect aids decision-making, and Rutina's initial noble-fueled defiance softens into submission after harem-initiated discipline. He introduces Earth-originated cooking and bathing practices, enhancing the harem's quality of life. His sexual stamina increases over time, enabling sustained encounters with multiple partners, symbolizing his deeper integration into this new existence.

Interpersonally, Michio balances affection with authority. Roxanne holds favored status due to her loyalty and leadership, while Sherry and Rutina contribute analytical and strategic insights. Miria and Vesta provide energetic and calming presences, respectively. His relationship with slave trader Allen remains transactional yet respectful. The harem dynamic reinforces his role as a benevolent leader who values their input, maintaining hierarchy through nightly rituals and shared baths that foster group cohesion.