So far, there are three "episodes" in the series:
Episode 0, which is counter-intuitively the second novel released, is a short "fandisk" that takes place before the events of episode 1, and gives the player character's sister a much larger role. It's also somewhat of a showcase of new features not present in the first game, which include the ability to directly interact with the cast by clicking on them.
Episode 1, the first novel released, centers on the characters Chocola and Vanilla, whom the main character lives with, sleeps with and eventually has sex with. While Chocola and Vanilla are the main characters, the novel also includes a supporting cast of four other cat girls and the player character's sister.