The player takes the role of Sakuragi Kouji. Our protagonist is a senior in high school that at one point was the ace of his school's baseball team. An injury forced him into early retirement, crushing his dreams of becoming a professional baseball player. For the last five years Kouji and his dad have been living in an apartment building where, as time passed, the tenants of his floor became something like a surrogate family. Kouji and his dad, wedding dress designer Ryouko and her daughter Koyuki, and university student/ero-literature author Kaori.

Much to Kouji's dismay, his dad has a bit of a reputation as a womanizer, and most expect him to be a chip off the old block. Proving them wrong, Kouji is more serious than his dad, and already has his heart set on someone. Of course, the person Kouji is set on is (true to the game's title) Ryouko, surrogate mother of the tenants on the fifth floor, and Koyuki's mom.

While the plot focuses on the affair between Ryouko and Kouji (and all the trouble our couple goes through to keep it a secret from others), the game has a total of five heroines for us to get to know in this strange romantic comedy.