Cohabitation) is a Japanese adult social simulation game developed by Tactics, a brand of Nexton.

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.

The player assumes the role of protagonist Masaki Yamada who is living with Manami shortly after they have graduated from high school.

Four of the staff that created the game—Itaru Hinoue, Shinji Orito, Miracle Mikipon, and Shinory—later became four of the founding members of the visual novel brand Key.

Throughout gameplay, the player is given multiple options to choose from, and text progression pauses at these points until a choice is made.

The story begins on Sunday September 14, 1997 with two main characters shortly after graduating high school who are living together.

Planning was headed by YET11, who also did programming, and Don, who wrote the scenario,[2] though this person did not contribute in future Tactics titles.

[7] DMM released Dōsei Memorial Collection as a downloadable edition compatible with Windows XP on June 3, 2011.