Nanaki Moriyama attends school alongside Illyasviel von Einzbern, Miyu Edelfelt, Chloe von Einzbern, Suzuka Kurihara, Tatsuko Gakumazawa, and Mimi Katsura, counting them as friends. She maintains a typically laid-back and caring demeanor but exhibits a quick temper when provoked, especially in matters concerning her older sister, Nanami Moriyama. This protectiveness stems from an incident where Rin Tohsaka and Luviagelita Edelfelt’s conflict resulted in Nanami being targeted with live frogs, instilling a lasting phobia. Nanaki consequently harbors resentment toward Rin and Luvia for causing her sister distress.

Her family lineage possesses innate physical capabilities, though these generally remain dormant. Nanaki demonstrates exceptional martial arts talent, mastering the Gakumazawa Style with minimal effort and defeating the adult instructor who taught her. Illya observes this as a natural combat genius despite her youth.

Within the narrative, Nanaki primarily features in school life and comedic segments. She joins group activities like beach trips, festivals, and school events, including an OVA centered on a sports festival. Her most notable role occurs in the special episodes "Otome yo Toushi wo Isake" (Zenpen and Kouhen) from the *Fate/kaleid liner PRISMA☆ILLYA 2wei Herz!* Blu-ray releases, where she participates alongside Illya, Chloe, Luvia, Rin, Nanami, Tatsuko, and a cat named Gouto. These episodes adapt bonus chapters from the *3rei!* manga without contributing to major plot developments.

Nanaki’s role remains consistent across the series, films, OVAs, and spin-offs as part of Illya’s social circle. She provides occasional comedic or situational interactions, with no significant character development or expanded background beyond her school life and protective relationship with Nanami. Her family history and latent abilities receive no deeper exploration.