Miroku Fujima operates as an Interrogation Officer within the Spirit World Warriors Society, initially projecting a calm and likable demeanor that conceals his manipulative and deranged core. Obsessed with youmu as instruments to reshape the world through human darkness, his background includes an unaffiliated period before joining the society to advance his destructive agenda. He shares significant history with Izumi Nase, expressing peculiar interest in her beauty. He implanted a specialized tentacle-like youmu into both their eyes, fulfilling Izumi’s reluctant request for youmu understanding while creating a conduit to seize control of her body later.

During the Hollow Shadow incident, Miroku secured Izumi’s permission to observe the youmu within the Nase domain. He manipulated Sakura Inami’s grief over her sister’s death, supplying a weapon to absorb youmu essences. Though his plan to eliminate Mirai Kuriyama failed, he reclaimed the weapon and its accumulated energy, attempting to destabilize the "Beyond the Boundary" youmu within Akihito Kanbara. Thwarted by Akihito, Mirai, and other warriors, he still exposed Izumi’s youmu-infested state, causing her disappearance.

Physically defeated but prepared, Miroku’s consciousness merged with Izumi via the implanted youmu. For a year, they spread parasitic youmu worldwide, slaughtering Spirit World Warriors and transforming them into shadows. Exploiting Mirai’s amnesia, he contacted her under the guise of revealing Blood Clan lineage—a ruse to infect her. Impatient, he disguised himself as Akihito, assaulted Mirai at her apartment, infected her, and abandoned her to the youmu’s corrupting influence.

His endgame involved luring Akihito, Mitsuki Nase, and Shizuku Ninomiya to his decayed body in an atrium. A prerecorded message declared humanity’s inevitable fall to darkness, leaving only him and possessed Izumi conscious. As the merged entity arrived to fight, Hiroomi Nase freed Izumi while Akihito liberated Mirai. Expelled from both hosts, Miroku’s consciousness permanently vanished as the parasitic youmu disintegrated.

A formidable combatant, Miroku matched Izumi Nase or Ayaka Shindou (youmu-form) in swordsmanship and demonstrated hand-to-hand proficiency. His expertise included specialized youmu knowledge, particularly of Beyond the Boundary, and surgical skill evidenced by the parasitic implant. In the Mirai-hen film, his appearance shifted drastically: a grey hooded robe concealed his face, an eyepatch covered his left eye—consumed by glowing purple tentacles—and severe burns rippled across the left side of his head.