Tenchi Muy?! Ry?-?ki is based on the manga and anime series Tenchi Muyo, in particular the 20-episode OVA Tenchi Muyo: Ryo-ohki (same name as the game, but with a slightly different official romanization). The story centers around a seemingly ordinary boy Tenchi Masaki, who lives in the countryside on the Earth. After accidentally releasing a spaced pirate named Ryoko, his modest house attracts the attention of powerful people from space, including an officer of the Galaxy Police, a famous scientist, and two sisters from a royal family in search of their long-lost half-brother. Soon Tenchi finds out the truth about his own identity and his super-powers, but still can't quite handle a household with five attractive young women, some of which seem to have a special interest in him...

The game is a traditional Japanese-style adventure: no puzzles, but many situations during which the player has to make choices. These choices lead to branching story lines, which in their turn lead to different endings. The game is viewed from first-person perspective, beside navigation around Tenchi's house, which uses a platform view.