Anastasia Nasuhara is a student at Saint Liliana High School, where she is in her second year and holds the position of student council vice-president. She comes from an exceptionally wealthy family, being the daughter of the owner of Nasuhara Industry, a worldwide conglomerate. Her heritage is mixed, with both Russian and American parents, giving her a cosmopolitan background. Due to her father becoming the head of the family, she moved to Japan at the age of five and transferred into the lower division of Saint Liliana Academy, where she has remained ever since.

In terms of personality, Anastasia is known for her cool and often expressionless demeanor. Her tone and facial expressions frequently lack overt emotion, which can make her seem distant or unapproachable. She has a habit of asking very direct and strange questions without hesitation. A prime example of this is upon first meeting Akito Himenokouji, when she immediately asks him if he is a virgin. Despite her cold exterior, she is not entirely aloof and has a hidden fondness for cute and flashy things. Her room is filled with numerous plush dolls, and she has a particular fondness for stuffed bears. She also enjoys playing with Arisa, a young girl, further showcasing this softer, more playful side that she typically tries to keep concealed.

Anastasia's motivations and role in the story are heavily centered on her relationships with the main characters. She is established as a rival to Akiko Himenokouji, taking pride in the fact that she surpasses Akiko in several measurable areas, including height, grades, and even breast size. She also notes her higher rank in the student council and her placement in the Miss Saint Liliana High School election. This rivalry is a consistent dynamic in her daily life. However, her attitude towards Akiko's brother, Akito, is markedly different. For reasons that are not immediately clear, she feels no排斥 (resistance or discomfort) towards him and gets along with him very well. On his very first day transferring to the school, she confesses her feelings for him, though the chaotic circumstances that follow prevent him from giving her an answer. She develops a close relationship with Akito and insists that he call her by the nickname Anna. She takes advantage of the fact that Anna sounds identical to the Japanese word for hole (穴, ana), teasing him about calling a girl a hole whenever he uses the nickname. Her feelings for him continue to develop, and she eventually proposes that they date with marriage in mind.

One of Anastasia's most notable weaknesses is her complete inability to perform household chores. Due to being raised in a wealthy family where she never had to do such tasks, she is extremely bad at cooking, cleaning, and even simple tasks like weeding a garden. She is openly aware of this deficiency and makes no effort to hide it, often gladly admitting her incompetence in this area to avoid doing work. As for other abilities, she is highly intelligent, as evidenced by her academic record, which is superior to her rival Akiko. Her role as student council vice-president also implies a degree of organizational capability and responsibility within the school's administrative body. She also has a peculiar talent for inserting jokes and puns that she likes into conversations, particularly those that elicit an annoyed reaction from Akito.