Boku no Natsuyasumi 4: Setouchi Shōnen Tanteidan - "Boku to Himitsu no Chizu"

Boku no Natsuyasumi 4 is the fourth main game in the life simulation series of spending an August summer vacation in Japan. This time the young boy grader Boku spends his summer vacation in a coastal town, similar to Boku no Natsuyasumi 2. It is also the first game in the series not to be released for consoles, but only for handheld devices. He is still in fourth grade like the previous games, so once again it is an alternate universe sequel, except this time it is set ten years later: in 1985.

The game closely follows the original design. Boku has only 31 days where time passes in real-time as soon as he moves to a new screen. The game consists of fixed screen, pre-rendered environments with 3D models and a cinematic camera with a different viewpoint for each scene. The player is free to choose how to spend his time as it is presented as a sandbox environment. Many activities from the previous games return such a bug collecting, sharing family meals, doing morning exercises and fishing, but there also new activities such as playing several table top games, organizing a beetle circus, challenging other children to duels with mechanical toys and playing a taiko drum.

Many scenes offer interaction for the sake of exploration, with no further purpose. Time advances when a new scene is entered, so it is not possible to complete all content in a single playthrough.