Mima Kirigoe, an aspiring actress and former member of the J-pop idol group CHAM!, makes the bold decision to leave her music career behind. This transition, however, does not sit well with all of her fans, particularly an obsessive admirer named Mamoru Uchida, famously known as Me-Mania, who begins to stalk her after feeling betrayed by her change from a wholesome image. Amidst the chaos, Mima stumbles upon a website titled "Mima's Room" filled with unsettlingly detailed diary entries that reflect her thoughts and daily life, igniting her anxiety.
As she navigates her new path in acting, she is supported by her manager, Rumi Hidaka, and her agent Tadokoro. Mima confesses her concerns about "Mima's Room" to Rumi, who advises her to disregard it, urging her to focus on her work instead. Mima's first significant acting challenge comes with a role in the television drama Double Bind, where she is thrust into a larger and more distressing part that includes a rape scene. Despite Rumi's strong reservations, Mima chooses to accept the role, which plunges her deeper into mental turmoil.
While filming, Mima experiences disturbing visions of her previous self in her idol attire, claiming to be "the real Mima." This blurring of reality and performance is exacerbated by her feelings of guilt over leaving her idol group and the constant dread of being stalked, leading her to suffer from severe psychotic episodes. As the project progresses, a series of murders connected to her work unfold, and Mima finds herself at the center of a chilling mystery, unsure of her own innocence when she recalls a night when she believed she murdered a photographer named Murano.
Mima’s struggles culminate in the intense filming of Double Bind, where her character's dark fate is revealed—having killed and usurped her sister’s identity due to underlying trauma. When an attempt on her life is made by Me-Mania, acting on delusions fueled by "the real Mima," she retaliates, knocking him out with a hammer. Moments of shocking clarity bring her to confront the horrifying truth surrounding the identity crisis she faces.
After the harrowing incident, she is rescued by Rumi, who leads her to a room mimicking Mima's own, revealing that she orchestrated "Mima's Room" and the associated murders, driven by a warped desire to reclaim her idol’s perfection. The two engage in a frantic confrontation, where Mima accidentally incapacitates Rumi, who is left overwhelmed by her delusions. Just as Rumi threatens her future, Mima saves her from an oncoming truck, a moment that brings an end to her nightmarish visions.
With time passing, Mima has risen to fame as an accomplished actress and decides to visit Rumi in a mental institution. During this visit, Rumi’s doctor reveals that she is trapped inside her own world, still believing she is a pop idol. Mima reflects on the growth she has experienced due to their tumultuous relationship. However, as she exits, she overhears nurses questioning whether she could be a mere lookalike of the "real" Mima Kirigoe. Mima, revitalized and confident, smiles at her reflection in the car mirror, affirming her identity with the declaration, > "No, I'm the real Mima Kirigoe."
