Shouko Nishijima serves as Sae Kusunoki's best friend and adjacent desk mate at school. Initially oblivious to Sae's hidden life as a magical girl, Shouko’s own latent magical potential surfaces when she unexpectedly perceives the fairy Emitto. Though evaluated as having lower magical aptitude than Sae, this revelation fuels Shouko’s determination to form a contract and become a magical girl. Her resolve crystallizes upon learning of Sae’s past hardships—stories Sae shared hoping to dissuade her. Instead, they inspire Shouko to vow protecting Sae out of gratitude.

This gratitude partially originates from Sae’s role in rescuing Shouko’s father, who had lapsed into an unexplained coma after a consciousness-draining magician—later defeated by Sae—targeted him. Hailing from a wealthy family, Shouko nurtures eclectic interests spanning traditional Japanese arts like Ikebana, anime, and a specialized passion for militaria. This fascination with military hardware directly shapes both her magical combat approach and Sae’s; she sparks Sae’s ability to conjure heavy weaponry through magic. As a magical girl, Shouko similarly summons heavy armaments in combat.

She battles alongside Sae daily against "Violators"—interdimensional entities from Eterland assaulting Shirakaba Academy. During these clashes, where Violators frequently deploy sexually charged tactics, Sae undergoes a burgeoning awareness of her own sexuality. While centering on Sae, this development unfolds against the backdrop of their joint confrontations with these adversaries.