Ikari Yaoroshi is a seventeen-year-old student at Rasetsu Academy and a classmate of the protagonist, Shiki Ichinose. He has a memorable appearance characterized by his black hair, blue eyes, and the distinctive piercing on his left eyebrow, which is a keepsake from his late mentor, Tenma. His birthday is November 11.

Personality wise, Ikari is defined by his explosive temper and confrontational manner of speaking, often appearing to be perpetually irritated and seeking conflict. However, beneath this aggressive exterior lies a surprisingly pure and naive core. He is notably uncomfortable with sexually explicit conversation and revealing clothing, often becoming flustered in such situations. Holding a deeply conservative view on relationships, he sincerely believes that a man and woman should not live together until after they turn twenty, a principle he learned from an older figure named Kajiki. This combination of hot-blooded aggression and unexpected innocence creates a distinct and often contradictory personality.

The driving force behind Ikari's actions is a deep-seated need for revenge. As a child, both of his parents were murdered by a Momotaro, the traditional enemies of the oni. After becoming an orphan, he was taken in by a delinquent gang known as Team Wild Fist, led by Tenma. Ikari found a new family with Tenma and his comrades, but tragedy struck again when another Momotaro attack left Ikari as the sole survivor of the massacre, a trauma that left him burdened with guilt. This loss forged his primary goal in life: to kill as many Momotaro as the number of comrades he lost. This vow is what motivated him to enroll in Rasetsu Academy, a school for oni, to gain the power necessary for his vendetta.

In the story, Ikari begins as a fiercely independent and vengeful loner, distrustful of groups and larger ideals. He participates in several major arcs, including the conflict in Kyoto where he fights against the Agri group alongside Jin Kougasaki. During the Nerima arc, under the alias Shinji, he faces the powerful Osuke Momokado. Though initially overwhelmed and nearly killed, he awakens a powerful winged form of his ability to win a desperate victory, leaving his left arm severely injured. His obsession with growing stronger leads to reckless behavior during the snowy mountain training arc, where his selfish actions are harshly criticized, though he ultimately reaches the summit with the support of his friends. Later, feeling his values no longer align with Rasetsu Academy, he leaves to become a temporary ally of the Oni Nation Squad. However, after witnessing the squad's merciless slaughter of non-combatants, he rejects their ideology as well and decides to walk a solitary path to liberate oni from their oppression. A pivotal moment occurs when he is cornered by the Momonoki brothers; Shiki Ichinose arrives to save him, and Shiki’s unwavering friendship helps Ikari realize his true fear is losing his comrades again. This emotional awakening unlocks an evolved form of his ability, allowing them to defeat their enemies together. After the conflict, he apologizes to his previous mentor, Naito Mudano, and is allowed to return to Rasetsu Academy, having matured significantly.

His key relationships are central to his development. His bond with Shiki Ichinose is the most important, transforming from simple classmates to close friends and trusted partners who help each other grow. He shares a rivalry and occasional alliance with Jin Kougasaki. Tenma remains his most influential figure, as his mentor's memory and the piercing he left behind are constant reminders of Ikari's past and his vow for vengeance.

Ikari's notable abilities stem from his Blood Release technique known as Doki Doki Hysteria, a power fueled by his anger. The unique and often frustrating aspect of this ability is its inherent randomness; even Ikari himself does not know what will be created each time he uses it. He can only activate this ability three times per day, and if a created weapon is destroyed, he cannot remake it that day. Over the course of the series, he manifests a wide array of items, including boots that enhance his kicking power, a powerful clawed gauntlet, a pair of twin holy blades, giant bird-like wings that allow for flight and projectile attacks, and a large scythe. His most powerful techniques include the Fallen Angel's Roar, a devastating tornado unleashed from his winged form at the cost of his own blood, and the evolved form Doki Doki Hysteria Modified: Lightning Speed Modified, which manifests a highly modified motorcycle equipped with various functions, symbolizing his inheritance of Tenma's will. As his character shifts from pure vengeance to protecting his friends, his power increasingly responds to his desire to shield his comrades rather than just his rage.