Dōsei (同棲, lit. Cohabitation) is a Japanese adult social simulation game developed by Tactics, a brand of Nexton. It was released on May 23, 1997 for Windows PCs, the same day as To Heart by Leaf. The gameplay in Dōsei follows a branching plot line which offers pre-determined scenarios with courses of interaction, and focuses on the appeal of the sole female main character Manami Minase.