From the Super Mario Wiki
A person of randomly chosen gender is hanging on a zip wire and the player, controlling the other of the pair, has to help him or her by tilting the Wii Remote or Nintendo 3DS left or right. This makes their partner move towards the island so they can reunite. In later levels, there are whales spouting water (aliens shooting laser beams in WarioWare Gold). If the person gets caught in these, they are sent off and the game is lost.
In WarioWare Gold, the characters are a princess and a prince (named Long-Lost Love and Distant Darling respectively in the Wario Kard mode), recurring characters in the game who also appear in Rocky Reunion, Long Lost Love, Love Tester and Hookin' Up.