Yuuki Wakura, a third-year high school student living an ordinary life, was transported to the demonic dimension Mato during a random gate appearance. Facing death from Shuuki monsters, he was rescued by Kyouka Uzen, commander of the Anti-Demon Corps' 7th Unit. To survive, he agreed to become her "slave," binding himself through a supernatural contract. His childhood was defined by training under his older sister, Aoba Wakura, who taught him exceptional housekeeping, cooking, and combat skills via a point-based reward system. This upbringing made him an adept caretaker. Aoba disappeared six years prior during a Mato disaster, an event that deeply affected him and fueled his motivations. As Kyouka's slave, Yuuki transforms into a powerful, humanoid Shuuki-like creature by performing a submissive gesture, typically kissing her hand or boot. This base "Slave Form" grants superhuman strength, speed, durability, and shockwave generation. It features a horned canine-reptilian face, tribal markings, samurai-style pants, and a chained collar controlled by his master. If Kyouka is absent, partial transformations using her belongings offer weaker, temporary power. Kyouka's ability allows "Lending," enabling other Peach-blessed women to become Yuuki's temporary masters. Each master alters his form and abilities: - **Himari Azuma (Whirlwind Form)**: Enhances speed and agility with a scarf-like feature, reducing raw strength. - **Kyouka & Himari Combined (Warcloud Form)**: Grants overwhelming power and a destructive breath weapon ("Howling"), causing severe exhaustion. - **Nei Ookawamura (Sparkling Stars Form)**: Boosts sensory perception to clairvoyant levels at the cost of physical prowess. - **Ren Yamashiro (Killer Fang Form)**: Triggers a berserk state with heightened regeneration, eroding rationality and causing indiscriminate attacks. After battles, the slave contract enforces involuntary "rewards" reflecting Yuuki's subconscious desires, often intimate acts like kissing or physical contact. Though initially embarrassed, he grows accustomed to these over time; masters cannot resist fulfilling his wishes. Personality-wise, Yuuki is idealistic, earnest, and chivalrous. He struggles with societal gender inequality preventing men from gaining powers from Mato's Peaches but finds purpose protecting others. Initially awkward around women due to limited prior interaction, he develops confidence through bonds with the 7th Unit. His core drive shifts upon discovering Aoba survived as a humanoid Shuuki leader; he vows to save her and reverse all such transformations. His combat abilities evolve through training and lending experiences. He masters techniques like the "Great Cross Edge" (a joint slash with Kyouka) and "Tenshin" (a controlled, enhanced state). Later, he gains accelerated healing from absorbing thunder god essences. Non-transformed, he utilizes his sister's combat training and tactical ingenuity. Yuuki resides in a mental "Dream Land" mimicking the 7th Unit's dorm. This space later houses the soul of Kuusetsu, a deceased thunder god, and becomes integral to his psychological resilience.