"Norn9: Norn + Nonette" is a science fiction anime series based on the otome visual novel of the same name. The story is set in a futuristic world where humanity has achieved advanced technology, including the ability to travel through the skies in airships. The narrative revolves around a group of individuals aboard a mysterious airship called the Norn, which is on a journey with an unknown destination. The passengers include three young women—Koharu, Nanami, and Mikoto—each possessing unique abilities, and nine young men, all of whom are connected to the ship's enigmatic mission.

Koharu, a cheerful and innocent girl, is discovered by two of the male passengers, Sorata Suzuhara and Itsuki Kagami, in a remote village. She is invited to join the Norn, where she learns that she is one of the "Witches," individuals with special powers. Nanami, another Witch, is reserved and struggles with her identity, while Mikoto, the third Witch, is calm and composed but harbors her own secrets. The nine men aboard the ship, including Sorata, Itsuki, and others like Kakeru Yuiga and Senri Ichinose, each have distinct personalities and backgrounds, often clashing or forming bonds as they navigate their shared circumstances.

The plot unfolds as the group grapples with the purpose of their journey and the true nature of their abilities. The Norn is guided by a sentient entity known as "The World," which communicates cryptic messages and tasks to the passengers. As the story progresses, tensions rise among the group, fueled by mistrust, hidden agendas, and the revelation of past traumas. The Witches' powers, which include manipulating time, space, and matter, become central to the unfolding mystery, as their abilities are tied to the ship's ultimate goal.

Throughout the series, the relationships between the characters are explored in depth, with romantic subplots emerging between the Witches and the male passengers. These relationships are shaped by the challenges they face, including external threats and internal conflicts. The narrative delves into themes of identity, destiny, and the consequences of wielding great power, as the characters confront their fears and desires while striving to uncover the truth about the Norn and their roles in its mission.

The story is structured around multiple perspectives, allowing for a nuanced exploration of the characters' motivations and backstories. As the Norn's journey progresses, the passengers are forced to make difficult choices that test their loyalties and resolve. The series combines elements of mystery, romance, and science fiction, creating a layered narrative that keeps viewers engaged as the characters' fates intertwine with the ship's enigmatic purpose.