"Zaion: I Wish You Were Here" is a four-episode original video animation (OVA) series that blends science fiction, action, and psychological drama. The story is set in a near-future world where humanity faces an existential threat from a mysterious alien entity known as NOA. NOA is a sentient, virus-like organism capable of infecting and controlling human hosts, turning them into aggressive, destructive beings. To combat this threat, the global organization CURE deploys advanced technology and a specialized combat unit called the Zaion Team.

The protagonist, Mai Hasegawa, is a young woman who becomes a key figure in the fight against NOA. Mai is initially an ordinary civilian but is drawn into the conflict after a chance encounter with the Zaion Team. She possesses a unique genetic trait that makes her immune to NOA's infection, a trait that becomes crucial in developing a countermeasure. As the story progresses, Mai is recruited into the Zaion Team, where she undergoes rigorous training and faces the psychological toll of battling an enemy that can manipulate human emotions and memories.

The Zaion Team is equipped with advanced combat suits and weaponry designed to neutralize NOA-infected hosts. However, the team faces constant challenges as NOA evolves and adapts, making it increasingly difficult to predict and counter its actions. The narrative explores themes of identity, loss, and the ethical dilemmas of using advanced technology to combat a seemingly unstoppable force. Mai's journey is marked by her struggle to reconcile her humanity with the demands of her new role, as well as her growing bond with her teammates, who each carry their own burdens and motivations.

The series builds tension through its portrayal of NOA's relentless threat and the personal stakes for the characters. The final episodes escalate the conflict, culminating in a high-stakes confrontation that tests the limits of the Zaion Team's resolve and technology. The story concludes with an open-ended resolution, leaving room for interpretation regarding the future of humanity's struggle against NOA and Mai's role in it.