Anastasia is a female ninja and a key figure among the ten warriors gathered by the warlord Sanada Yukimura. She is a young woman with blue eyes and long blonde hair, which she typically ties back in a ponytail. Her combat skills are defined by her mastery of ice-based magic, earning her the epithet of Ice Flower. She is capable of freezing water and mist in an instant and employs a range of offensive techniques given names such as Extreme Ice Coffin, Ice Burial, and the secret art known as Permafrost.

Anastasia hails from the Iga province, where she was trained as a kunoichi, or female ninja. She shares a deep personal history with another member of the Braves, Saizo Kirigakure, as the two are childhood friends who grew up together in the same ninja clan. Her personality is dual-layered; she can be clever and enjoys playful teasing in casual moments, but she becomes completely serious and focused when engaged in battle. This playful demeanor often manifests in her interactions, such as when she comments on the physical attributes of other female members of the group.

Her true motivations and loyalties are complex and form a major turning point in the narrative. While she initially appears to be a loyal ally to Yukimura, it is eventually revealed that her original mission was to assassinate him. Furthermore, she was secretly acting as a spy for a rival faction, making her a genuine threat from within the group. Her primary mission as a spy was to steal the special magical eye belonging to another warrior, Rokuro Unno. In a critical confrontation, she attacks Rokuro, leading to a struggle in which he destroys his own eye to prevent its secrets from falling into her hands.

Throughout this betrayal, Anastasia demonstrates a strong sense of purpose, yet her history with her comrades complicates her actions. When confronted by her childhood friend Saizo, she warns him to stay away to avoid having to kill him, showing she still harbors some regard for him. Despite her formidable ice magic, which allows her to momentarily trap the ninja Sasuke Sarutobi, she is ultimately outmatched by Saizo's superior speed and skill. During her fight with Saizo, she uses her powers to freeze a nearby lake as a distraction to escape, though it is later implied that Saizo deliberately allowed her to flee. Her role in the story is therefore that of an infiltrator whose betrayal forces the group to confront the harsh realities of espionage and tests the bonds of trust between its members. Her ultimate allegiance is to her own mission and, later, to the enigmatic Hattori Hanzo, whom she serves as a key operative.