Dōsei

Dōsei is a romance social simulation game in which the player assumes the role of Masaki Yamada. Much of its gameplay is spent on reading the story's narrative and dialogue. Dōsei follows a branching plot line with multiple endings, and depending on the decisions that the player makes during the game, the plot will progress in a specific direction. Throughout gameplay, the player is given multiple options to choose from, and text progression pauses at these points until a choice is made. To view all plot lines in their entirety, the player will have to replay the game multiple times and choose different choices to further the plot to an alternate direction.

The story begins on Sunday September 14, 1997 with two main characters shortly after graduating high school who are living together. They are, the protagonist Masaki Yamada (山田 まさき, Yamada Masaki) and the heroine Manami Minase (皆瀬 まなみ, Minase Manami) who he is living with; both characters' names can be altered to anything the player chooses. There are two parameters related to Masaki and Manami which change depending on decisions the player makes during gameplay. Masaki's parameters are physical and emotional strength, and Manami's parameters are degrees of affection and lewdness. How much money the protagonist has from his job is also a factor in the game; the player starts out with 100,000 yen.

Dōsei was Tactics's first game. Planning was headed by YET11, who also did programming, and Don, who wrote the scenario, though this person did not contribute in future Tactics titles. Art direction and character design was headed by Itaru Hinoue, and was the second time she had ever contributed in a visual novel. Hinoue also contributed with the computer graphics along with Miracle Mikipon, Shinory, and Suō Akiyama, and Mikipon also worked on the game's animation sequences.

The music in the game was mainly composed by Shinji Orito who had at the time moved to Tactics after working under Leaf for three games. Hinoue, Orito, Mikipon, and Shinory later became four of the founding members of the visual novel company Key founded in 1998. Three others—Myū, Paste, and Ishisan—also helped with the music, but between them only composed one third of the game's soundtrack.