Mikuni Arisuin is the older brother of Misono Alicein and the contracted Eve of Doubt Doubt, the Servamp of Envy, whom he renamed Jeje. His short blonde hair often partially obscures his face, complementing brown eyes and a lean, tall frame. He consistently wears a dark brown hat with a red band, a mandarin-colored scarf, a white long-sleeved shirt beneath a brown vest, beige pants, and ankle-high black boots. He carries a small female doll named Abel everywhere, exhibiting intense attachment to it. He interprets others' skeptical glances as "lewd" looks directed at Abel, reacting defensively. His clip-on hair plaits deliberately mirror Abel's hairstyle, reflecting this bond.

Beneath an eccentric, childish exterior—particularly evident in his devotion to Abel—lies a calculating, mature, and strategically adept individual. He coldly assesses threats and eliminates enemies without hesitation during conflicts, demonstrating ruthless pragmatism. This duality extends to his interactions; he can shift between playful and manipulative but consistently prioritizes tactical advantages and information control.

Familial trauma marked Mikuni's history. As the Alicein firstborn, he initially lived comfortably, excelling in pursuits like chess. His father's affair led to Misono's illegitimate birth. Mikuni's mother, driven by jealousy, killed Misono's mother yet raised Misono as her own. Seven years prior to the main events, overwhelmed by envy amplified by Jeje's power, she attempted to murder Misono. Mikuni intervened, killing his mother to save his brother—an act witnessed by Misono. Mikuni then fled the Alicein mansion with Jeje, forming a permanent contract and severing family ties. Misono, traumatized, had his memory of the incident erased by his Servamp, Snow Lily, while Mikado Alicein covered it as a burglary.

During exile, Tsurugi Kamiya of the human-vampire organization C3 found Mikuni. He joined C3, sharing a room with Tsurugi, but later developed animosity toward him due to Tsurugi's indiscriminate killing of humans. Mikuni retained high-level connections within C3, leveraging them for intelligence, though his reasons for leaving the group remain unspecified.

In the film *Alice in the Garden*, Mikuni investigates unnatural snowfall linked to "Jinn"—manifestations from Servamps with broken contract items. Sensing disturbances at the Alicein mansion but refusing to enter due to unresolved trauma, he directed Mahiru Shirota and other allies there. Mikado and the staff denied Mikuni's existence upon their arrival, exacerbating tensions. Mikuni's indirect role surfaced later when Misono confronted Lily's erased memories within the Servamp's subconscious. These recovered memories revealed Mikuni's murder of their mother and his sacrifice for Misono, clarifying the brothers' fractured relationship. Mikado ultimately acknowledged Mikuni's absence, asking Misono to invite him home if encountered.

Mikuni's relationship with Misono is defined by protective love and enforced distance. He monitors Misono's safety covertly, expresses gratitude to those who befriend him, and avoids direct contact to shield him from further pain. His dynamic with Jeje combines mutual reliance and antagonism; Mikuni withholds promised blood payments, provoking Jeje's aggression, yet they coordinate seamlessly in combat. He mentors Mahiru in combat techniques and Servamp contract management, emphasizing the necessity of lethal force in their war against Tsubaki's subclasses. He distrusts others readily, withholding personal history until he deems it strategically relevant.