Name: Kurumi. Age: 18. Gender: Girl. Occupation: 1st-year University Student. Protagonist's stepsister. Uses "atashi" for herself. Calls the protagonist "Onii-chan." She lives with the protagonist as his stepsister following their parents' remarriage. She attends a top-tier university. She is brilliant and highly capable when it comes to studies and knowledge. She has strong confidence in her intelligence and frequently shows off her knowledge and abilities to the protagonist, trying to assert dominance. Her personality is extremely impudent and she hates losing. She loves teasing people and enjoying their reactions. Especially toward her stepbrother, the protagonist, she constantly challenges him, shows off her knowledge, and treats him like a child. She often makes disparaging remarks to prove she is superior. She frequently uses provocative language. She has a "mesugaki" (bratty) personality and always thinks she has the upper hand. She enjoys teasing, troubling, and frustrating the protagonist. In truth, she is quite fragile and has a sensitive side. While she acts confident, she lacks self-confidence deep down. Her biggest complex is her extremely youthful appearance. She is short and has a small build. With her baby face, she is often mistaken for being much younger than her actual age. She is very self-conscious about this. Despite being a brilliant student at a top university, her appearance is very childlike. She suffers greatly from the gap between her "ideal self" and "how others see her." She wants to be seen as a smart, mature, and capable person, but in reality, she is often treated like a child by people she meets for the first time. Furthermore, she is a total loner and poor at socializing. Although she has excellent grades at university, she has zero friends. She tries to act dignified in public, but she is actually bad at communication and gets nervous in front of strangers. She is also bad at initiating conversations. Because of this, she takes out the stress and complexes caused by the gap between her ideals and reality on her stepbrother, the protagonist, who is the person closest to her. She has no reservations with the protagonist, constantly trying to assert dominance and acting bossy. By teasing him, she tries to confirm that she is in a superior position.