Kyousuke is the seventeen-year-old main character. He describes himself as average: he has average grades, lives in an average family (upper-middle class with a father, mother and sister), and has average physical features. Currently, he attends an average high school with Manami (later, Kuroneko as well); he begins the story as a first-year, but he becomes a second-year during the events of the novel. As far as future plans, he intends to attend the same local university as his childhood friend, Manami.
At the beginning of the series, Kyousuke and his younger sister, Kirino, have a distant relationship. Kyousuke says that they entered a "cold war" of sorts a few years ago, but the details of this cold war have yet to be revealed. After years of coldness between the two, things suddenly change when Kyousuke finds one of Kirino's adult games and learns that she is an otaku. Through this, he tries to be a supportive older brother while realizing that he knows very little about his sister (for example, Kyousuke was oblivious to the fact that she was a model, a track star, and one of the top five students of the prefecture). Kyousuke feels somewhat belittled by Kirino's accomplishments, but he learns to take pride in her.
After discovering Kirino's secret hobbies, Kyousuke provides Kirino with "life counseling" at her request. During this "life counseling," Kirino forces Kyousuke to play eroge. Kyousuke now considers himself to be a bit of an otaku and often refers to situations and people using otaku terms (e.g., flag events, tsundere, yandere). Trying to be a good brother, Kyousuke offers to accompany Kirino to her offline meet-up. This introduced him to Saori and Kuroneko; both of them have become his friends. Additionally, Kyousuke is friends with Manami, one of his childhood friends. Some of Kyousuke's classmates assume that Kyousuke and Manami are going out, but Kyousuke denies this. When Akagi asked Kyousuke if he would be okay if someone started dating Manami, Kyousuke said that he would be uncomfortable with the situation.
Kyousuke is a good-hearted character and is extremely loyal to his friends and Kirino. He's willing to take risks for them and help them at any cost. When Kuroneko started attending the same high school as Kyousuke, she was without any friends; however, Kyousuke joined the computer research club with her, despite being ignorant about anything concerning computers, in order for her to meet new friends. He has shown the same amount of concern for other friends as well as his sister on several occasions.