Haruka, a sweet and innocent high school girl, is excited to meet her new stepbrother Tsukasa, who will be living with her while their parents are abroad. When they meet, Tsukasa, a young elementary school student, is even more adorable than Haruka had imagined. However, he has some unusual requests, seeking Haruka's help with his homework and wanting to sleep in her bed, which soon escalates into more intimate and provocative behavior.
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