Haruya Sakami serves as the human alias for Shutendoji, a high-ranking Oni tribe yo-kai operating covertly among humans. In this guise, he appears as a 13-year-old boy sporting messy black hair and blue eyes. His typical attire consists of a grey top layered under a dark blue jacket, black trousers, and distinctive blue jewelry—a bracelet and necklace. As a student, he wears a modified uniform with his shirt partially unbuttoned, retaining the blue bracelet.

Shutendoji's true form reveals a humanoid yo-kai with dark gray skin marked by light gray patterns, long red hair, golden-tipped horns, and striking white eyes featuring red pupils. He dons ornate clothing: a black shirt emblazoned with the kanji for "Heaven," baggy hakama pants, a gold neck cuff, and symbolic masks representing opposing forces—an Okame mask and a Hannya mask—embodying his ancient Oni heritage.

His primary mission targets a figure known as "the princess," believed to wield dominion over both human and yo-kai realms. To awaken her true power, he relentlessly pursues the five Sacred Swords. Infiltrating the human world, he enrolls in Summer Adams's school under the alias "Theo," aided by his subordinate Voidera disguised as teacher Ganryuu Shimanouchi.

Shutendoji exhibits a cunning, ruthless personality marked by scant empathy. He manipulates allies like the fortune-teller Sendo Rei and the yo-kai Fukurou, discarding them once their usefulness ends—such as stripping Rei of her clairvoyance after failure. He demonstrates lethal pragmatism, ordering Fukurou to eliminate Cole following the theft of the Sacred Sword Fudou Raimeinken.

His backstory reflects deep loyalty to the Oni tribe's cause. He initially obeyed a yo-kai possessing Isabelle, mistaking her for the princess. Discovering Summer Adams as Princess Shuka's reincarnation shifts his allegiance; he halts conquest plans at her request. Though his overenthusiasm irritates Summer, he proves genuinely helpful locating people or objects for her group.

A significant revelation occurs upon learning Natsume is *also* a reincarnation of Princess Shuka. This prompts him to attempt luring her to harness her power for domination, focusing purely on her strategic value despite peers speculating about romantic interest.

In combat, Shutendoji employs abilities like the multi-strike "Drunken Oni Fist" and "Super Sword Hunting," which saps enemy strength and spirit. His ultimate move, "Oni Shower," unleashes water-based magic degrading enemy stats. He also possesses the "Demon Blood" skill, enhancing strength and resilience at full health.

His evolved power manifests as the "Oni Kakusei Shutendoji" Awoken form, detailed primarily through game mechanics.