"Cosplay Girlfriend" centers on the relationship dynamics between its two main characters, Wataru Sasaki and Chizuru Mizuhara. Wataru is a reserved and introverted college student who struggles with social interactions and has little experience with romantic relationships. Chizuru, on the other hand, is a popular and outgoing cosplayer who works part-time as a rental girlfriend. The story begins when Wataru, seeking to overcome his loneliness and social anxiety, decides to hire Chizuru through a rental girlfriend service. Initially, their interactions are transactional, with Chizuru fulfilling her role as a professional companion. However, as they spend more time together, their relationship begins to evolve beyond its initial boundaries.

The narrative explores the complexities of their growing connection, blending elements of romance, comedy, and drama. Wataru’s awkwardness and genuine nature gradually break through Chizuru’s professional facade, revealing her vulnerabilities and personal struggles. Chizuru, despite her confident exterior, harbors insecurities about her identity and the pressures of maintaining her public image as a cosplayer. As their bond deepens, the story delves into themes of authenticity, self-discovery, and the challenges of navigating relationships in a world where appearances often overshadow reality.

Supporting characters, such as Wataru’s friends and Chizuru’s fellow cosplayers, add depth to the narrative, providing contrasting perspectives on love, friendship, and personal growth. The manga balances lighthearted moments with more serious explorations of emotional intimacy, creating a multifaceted portrayal of modern relationships. Through its focus on the evolving dynamic between Wataru and Chizuru, "Cosplay Girlfriend" offers a nuanced examination of how two individuals from different worlds can influence and transform each other’s lives.