Natsuki Shirafuji is a middle school girl and the deuteragonist of the series Saint October. She comes from a wealthy family and is best friends with Kotono Hayama, with whom she works as a detective at the Kuroki Detective Agency alongside Misaki Hijiri. Natsuki has very long blonde hair and blue eyes, and she is often seen wearing hair ribbons and stockings.

Natsuki's personality is marked by a strong sense of friendship and a degree of initial jealousy. When a young boy named Juan becomes the focus of Kotono's attention during a kidnapping case, Natsuki grows jealous of the time Kotono spends with him, leading her to attempt various schemes to frighten or eliminate Juan. However, after discovering that her friend’s care is all Juan has, she feels guilty and begins to warm up to him. Over the course of the series, she develops a more protective and supportive attitude toward her friends and allies.

Her motivations are closely tied to her loyalty to Kotono and her desire to protect those she cares about. As a member of the detective agency, she is dedicated to solving mysteries and fighting the forces behind the kidnappings. Her role in the story is that of a key ally and a second magical girl, joining Kotono in battle after receiving her powers.

Natsuki's notable abilities come from her association with the Moon tarot card. When she transforms, she becomes Loli White, a magical alter ego. Her weapon of choice is a pair of nun chucks, which she uses in combat. She gains her transformation powers from Juan, similar to how Kotono received hers. Throughout the series, Natsuki evolves from a somewhat self-centered and jealous girl into a more mature and cooperative fighter, strengthening her bonds with Kotono and the other characters.