My little sister: Prologue (itch)

Suhan, who goes to high school, is frustrated because he can't get along with his younger sister Sunmi. One day, he went to his friend Jinyong's house and saw Jinyong get along very well with his sister. To the envious Suhan, Jinyong pulls out a small stone, saying, 'I was never on good terms with my sister either, but this helped us get along.'

The stone had the mysterious power to change what had happened in the past. Suhan used stones to change poor Sunmi's memories one by one, and because of the changed past, he was able to get closer to Sunmi. Suhan fell in love with changing the past, and then things happened that never occurred...