Misty Mei began as Meimi Otonashi, a classmate of Naoto Jinno and Rika Manabe. Witnessing Naoto's romantic proposal to Rika in a park, Meimi retreated, consumed by jealousy. The demon Asmodeus exploited this vulnerability, transforming her into the demonic entity Misty Mei to serve as his subordinate targeting Rika for corruption, fundamentally altering her identity and allegiance.

As Misty Mei, her appearance diverges significantly: long teal hair, garnet eyes, functional bat wings, and attire typically including a mini-dress, collar, stockings, gloves, and a lolita-style hairband. Her personality shifts from Meimi's original shy and sweet nature to rude and sharp-tongued. Though nominally serving Asmodeus, she exhibits a volatile temperament, often disregarding hierarchy and treating him as "her slave." Her attacks deploy tentacle creatures to sexually assault victims, aligning with demonic corruption objectives.

Her arc involves repeated assaults on Rika and Naoto under Asmodeus's command using her tentacles. During one attack coordinated with the demon General Reirouge, Reirouge attempted to distract Naoto through seduction while Misty Mei ambushed Rika separately; this failed when Naoto broke away to rescue Rika. After Asmodeus's defeat, the demon Rococo captured Meimi Otonashi using the "Eternal Worm." The worm's special fluids forcibly separated Misty Mei from her human identity. Freed from Meimi's consciousness, Misty Mei captured Rika, enabling Rococo to transform Rika into "Dark Djibril" via similar parasitic means.

In the sequel *Djibril, the Second Coming*, Rococo further weaponized Misty Mei against the protagonists. Later, a mysterious photography student linked to Misty Mei's resurgence orchestrated attacks culminating in Hikari Jinno's abduction, with Misty Mei's direct involvement remaining implicit. Her fate remains unresolved across available media, with no definitive conclusion to her corruption or potential redemption.