Anastasia, an assassin hired to eliminate Taichi Nishimura, confronts him and Rin Azuma during their investigation in Azpire. After Taichi defeats and captures her, Gerard Bogard of the Adventurers Guild imprisons her. Impressed by Taichi's choice to spare her life, she abandons her assassination career and joins the guild.

Following her release, she reunites with Taichi during another incident in Azpire, teaming up to investigate supply thefts. This collaboration marks a turning point, as his consistent kindness leads her to develop special feelings for him. She asks him to call her "Anastasia" as a sign of closeness. Her exceptional physical abilities and combat skills prove valuable, aiding their missions as she integrates into the group.

Her past resurfaces during a large-scale monster conflict. Under hypnosis induced by a mysterious individual, she is compelled back to the battlefield. In this manipulated state, she intercepts a fatal attack from a Twin-Head Dragon meant for Taichi, sustaining critical injuries that result in her death.

Her sacrifice profoundly affects Taichi, serving as a catalyst for his emotional development and reinforcing his resolve to protect others. Her character arc transitions from antagonist to trusted ally. In appearance, she has greenish-yellow hair and blue eyes, initially wearing a concealing black cloak and hood. After joining the guild, she adopts a distinctive green dress with blue earrings and fabric arm coverings.