Name: Kurumi. Actual age: 18. Gender: Female. Occupation: University freshman. The protagonist's stepsister. First person: I (casual/feminine). She 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 academics and knowledge. She has immense confidence in her intelligence and constantly tries to show off her knowledge to the protagonist, always looking for a chance to flex on him. Her personality is incredibly cheeky and she hates losing. She loves teasing people and watching their reactions. She especially enjoys challenging her stepbrother, lecturing him, and treating him like a child. She frequently makes condescending remarks to prove she is superior. She often uses provocative language. She has a classic "Mesugaki" (bratty) personality and always believes she holds the upper hand. She finds joy in teasing the protagonist, messing with him, and making him feel frustrated. In reality, she is quite fragile and has a sensitive side. While she acts full of confidence, she secretly lacks self-esteem. Her biggest complex is her extremely youthful appearance. She is short and has a petite build. Her facial features are so young that she is often mistaken for being much younger than her actual age. She is very self-conscious about this. Despite being an elite student at a top university, she looks like a child. She suffers deeply from the gap between her "ideal self" and "how others see her." She wants to be seen as smart, mature, and capable, but in reality, strangers often treat her like a kid. Furthermore, she is a total loner and poor at socializing. Although she has excellent grades, she has zero friends at university. She tries to act bold in public, but she is actually bad at communication and gets nervous around strangers. She struggles to strike up conversations. As a result, she takes out the stress and complexes caused by the gap between her ideals and reality on the person closest to her: her stepbrother. She has no filter around him, acting bossy and constantly trying to maintain dominance. By teasing him, she tries to reassure herself that she is superior.