Chizuru Mizuhara, whose real name is Chizuru Ichinose, attends Nerima University as a literature major. She works secretly as a rental girlfriend for the Diamond agency under her alias "Mizuhara," funding acting lessons while maintaining a kind, considerate professional persona during rental dates. On campus, she adopts a reserved look with glasses and braided hair to avoid recognition.

Significant childhood trauma shapes her guarded personality. Losing her grandfather young led to deep attachment to her grandmother, Sayuri Ichinose, her sole remaining family. Her grandmother's later illness and death intensified Chizuru's emotional distance, prioritizing her acting career over personal connections due to fears of vulnerability and abandonment. Early experiences as a bullied "clingy crybaby" fueled her defensive "iron lady" facade.

Her character development centers on interactions with client-turned-neighbor Kazuya Kinoshita. Their transactional relationship evolves when Kazuya introduces her to his grandmother, a close friend of Chizuru's grandmother. They enter a fake relationship to maintain family appearances. Initially insisting on professionalism, Chizuru gradually develops genuine feelings for Kazuya. This conflict manifests as tsundere behavior: denying romantic interest, becoming argumentative or physically defensive when embarrassed, and hiding her blushing face. She corrects Kazuya calling outings "dates" and downplays gifts as reciprocity. Concurrent deredere traits emerge: initiating unpaid coffee meetings, expressing jealousy over Kazuya's interactions with other girls, and privately practicing saying his name without honorifics while blushing.

Key moments accelerate her emotional openness. After Kazuya saves her from drowning, she acknowledges her feelings while chastising herself as "an idiot" for falling for a client. His confession of love further breaks down her barriers. When their grandparents orchestrate closeness, like sharing a room during a trip, Chizuru agrees but lies awake thinking about him. Her grandmother's terminal illness and death become pivotal; Chizuru isolates herself but breaks down during a Kazuya-arranged fireworks display, crying in his arms and accepting his support. She later confesses never regretting meeting him, highlighting growing reliance.

Significant milestones include passionate public kisses to defend their relationship when exposed by Kazuya's ex-girlfriend Mami, and agreeing to a real, non-rental date. She still hesitates to fully articulate feelings but anticipates outings with visible excitement, blushing while checking her calendar. After an earthquake destroys their apartment complex, she moves in with Kazuya and neighbor Mini Yaemori, leading to increased closeness. During cohabitation, she shares her deepest secrets, lets Kazuya care for her when ill, becomes more physically comfortable like allowing close proximity while trapped in a shed, reveals personal insecurities like seeking validation about her appearance, and clarifies her ideal wedding centers on emotional significance rather than extravagance.

Her arc culminates in a blend of lingering tsundere tendencies and genuine emotional availability, illustrating a slow journey toward vulnerability and mutual trust.