Держись, Цуёси! Залезай в машину времени, Цуёси, и возьми себя в руки!

Tsuyoshi and his perverted friend Tsukasa stumble upon a time machine while running away from Tsukasa's little sister. Along with the time machine's inventor they accidentally travel 12 years to the past and meet their younger selves along with Tsuyoshi's sister who back then wasn't a violent tomboy like nowadays. (Source: MaouNemesis)