Boku no Natsuyasumi 2: Umi no Bouken-hen is the sequel to Boku no Natsuyasumi and has a similar concept. The nine-year-old city boy Boku once again spends his summer vacation in the countryside in 1975. It is a alternate universe sequel where the character spends his vacation with his family in a different location, but still meets many characters from the first game. The sequel is set in a Japanese southern coastal town on the tropical Izu Peninsula where his aunt and uncle have a bed and breakfast.

The game consists of fixed screen, pre-rendered environments with 3D models and a cinematic camera with a different viewpoint for each scene. Boku's vacation only lasts 31 days, but the player is free to choose how to spend his time as it is presented as a sandbox environment. It is possible to seek quests and help the people in town to solve their problems, but he can also choose to ride his bike anywhere, go bughunting, spend time fishing, dive into the ocean, launch a rocket, go on walk, play hide and seek, or play a mini-game of beetle wrestling. 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.