Itsuki is a 20-year-old author who has an obsession towards younger sisters. He is a novelist who debuted when he was in high school; all of his novels feature younger sisters as the heroine. In the span of five years, he has published 20 books, some of which have ranked in the top 10 weekly rankings for light novels on Oricon. Despite his success, his irrational personality and writing style has led to mediocre success compared to his fellow writers. His relationship with his father became worse when his father remarried to Chihiro's mother only three years after Itsuki's mother died. He admits having feelings for Nayuta but the reason he does not go out with her is because he wants his novels to be as famous as hers, and then tell him what he feels for her. He later begins dating Nayuta but they later break up.
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