Sweet Hamster Days is a newly approved full-motion video game where the player is reincarnated as a hamster named Hamta and is continuously cared for by three sisters who gaze into the camera while petting the player character. The game was initially rejected from Steam apparently due to concerns over sexually explicit imagery of real people, but was eventually approved after the developer revised the age rating and other details.

The unusual concept originated from two distinct sources: creator Katayama's experience wearing mascot costumes at a part-time job, where he observed that people naturally became friendlier when interacting with someone in costume, and his admiration for Grand Theft Auto 5's character-switching mechanic. Designer Oda described the game as a 'completely unprecedented genre' and 'being-taken-care-of adventure game.'