YU-NO: A Girl Who Chants Love at the Bound of This World (1997)

Yu-No: A Girl Who Chants Love at the Bound of this World is a Japanese visual novel/ point-and-click adventure game developed originally as an adult game. The game's protagonist travels between various parallel worlds in order to solve the mystery of his parents' disappearance. Although parallel worlds are not an unfamiliar concept in science fiction, the game uses concepts from physics, mathematics, philosophy, history and religion to construct a unique fictional universe. In particular, the A.D.M.S. or Auto Diverge Mapping System; which visually displays the branching parallel worlds/storylines as a tree, aids the player in navigation.

Storyline

Takuya Arima is a young student whose father, a historian who has conducted various researches, disappeared recently. During a summer vacation Takuya discovers a strange orb in his father's room, along with a letter containing information about the existence of a parallel world. At first Takuya doesn't take it seriously, but soon he realizes that he possesses a device that allows him to travel to an alternate universe. Is his father alive, after all? If so, where is he?