Hiroshi Karigari is a college student highly skilled in robotics but struggling with pronounced shyness and social interactions. His unexpressed romantic feelings for fellow student Marie stem from social awkwardness and a lack of confidence in forming genuine human connections. Seeking to circumvent the challenges of real relationships, Hiroshi applies his technical expertise to build an android replica modeled after Marie, intended as a companion embodying his idealized perception of a perfect partner.

This completed android, also named Marie, develops unexpected autonomy and emotional complexity, diverging from his original programming. To conceal the android's true nature, Hiroshi claims she is his younger sister, using their physical resemblance to support this cover story. This fabrication creates complications as both versions of Marie exist within his social circle.

His situation intensifies when Hibiki Kennou discovers the android's secret and leverages this knowledge to pressure Hiroshi into a romantic relationship, threatening exposure unless he complies. This manipulation forces Hiroshi into interactions that strain his limited social capacities.

Throughout these events, Hiroshi experiences internal conflict. His initial fixation on the human Marie becomes complicated by the android Marie's evolving personality and affections, creating ambiguity about where his genuine attachments lie. This emotional confusion remains unresolved, particularly as the OVA's concluding segments explore metaphorical themes of identity and desire without providing definitive closure to his relational dilemmas.

Interactions with both Maries and Hibiki expose Hiroshi's vulnerabilities and moments of growth beyond his initial characterization, including protectiveness and ethical consideration regarding the consequences of his creation on the android Marie's autonomy. However, his core traits of indecisiveness and social anxiety persist as defining features throughout the narrative.