Yu-No

While walking on a beach alone, young Takuya has a vision of a girl calling him "papa" and putting a ring onto his finger. Soon thereafter he discovers that the ring gives him the ability to instantly travel not only in space but even in time. He also discovers that the beautiful women around him, from his classmates to his own step-mother, know much more than they let him know... and that all of this somehow relates to his late father's scientific research.