Itsuki is the 20-year-old protagonist of the series 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 3 years after Itsuki's mother died.
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