No. 0, also called "No. Zero," is an artificial partner created by Akira Mizutame, a scientist facing professional setbacks after a string of failed inventions. She emerged from his project to develop a romantic companion, an effort suggested to improve his personal life. This process defines her initial existence as an artificial being programmed to serve as a girlfriend.

Her programming establishes a foundation of pre-set emotions and behaviors aligned with this designated purpose. Yet, her development centers on an internal conflict as she experiences the emergence of genuine feelings distinct from her coded directives. These self-discovered emotions create significant tension between her programmed function and her evolving sense of self. Her narrative core explores this struggle, depicting her evolution beyond an artificial construct into an entity grappling with authentic emotional experiences.

Her relationship with Akira is complex, marked by his own difficulties in forming connections. Her journey involves navigating this dynamic while reconciling her burgeoning autonomy with the expectations embedded in her creation. This culminates in an intense confrontation regarding her existence and the nature of her feelings, leading to an emotionally charged resolution. This climax addresses the central questions of love and authenticity between creator and creation.