Ayumi Murai is a blue-haired student at the academy with gray eyes and a slim build, typically seen in the school uniform of a miniskirt and necktie. She frequently consults classmate Kaori Saeki for tarot readings about her love life, specifically her crush on fellow student Asada. When the cards indicate Asada is already in a relationship, Murai pleads for Saeki to use black magic to make Asada fall for her or break up with his girlfriend, a request Saeki refuses due to the risks.

After Taki Minase overhears this conversation, he offers to help Murai using a paper doll charm. Following Minase’s instructions, she pricks her finger, writes Asada’s initial "A" in her blood on the doll, chants an incantation, and hides the charm in Asada’s bag. Shortly after, Asada encounters Murai in the hallway with his girlfriend and immediately confesses his love for her, leading them to engage in sexual activity publicly until interrupted.

In *Bible Black: La Noche de Walpurgis*, Murai asks Minase for another spell to enhance Asada’s sexual endurance, but he rejects her request. She later directs Minase to Saeki’s location and, in some storylines, is coerced by Inoue’s group into delivering messages under threat.

Her role expands in the sequel *Bible Black: The Infection*. One month after the initial events, Saeki reads her tarot cards again; Murai interprets the reading as a warning to guard against rivals for her boyfriend. Later, under magical influence, she professes attraction to Minase, leads him to the gymnasium storage room, disrobes, and offers herself to him. Depending on player choices, Minase may accept or reject her advances. If rejected, she reports the incident to art teacher Hiroko Takashiro, who erases her memory. If accepted, she claims envy toward Minase’s relationship with Kurumi Imari and engages in sexual activity with him.

Subsequently, Murai participates in sexual acts with multiple students in the art club room and is later seen performing oral sex on Minase alongside Saeki. She continues engaging in group activities until halted by Takashiro’s magic and joins a ritual orgy in the school basement aimed at resurrecting Reika Kitami.

Personality-wise, Murai exhibits gullibility in her belief in magic and reliance on Saeki’s tarot. She displays insecurity about her romantic prospects and expresses guilt over enchanting Asada that soon gives way to triumphant joy, even boasting about her "evil" allure. She is sexually active, mentioning daily encounters with her boyfriend while complaining about his endurance.

Trivia notes a name discrepancy: Minase initially identifies her as Ayumi Murai but later refers to her as Motoko Murai in the first game without explanation. Chronologically, she and Asada are the first characters depicted having sex in the series. In the first game, she is the only named female character not shown in sexual scenarios.