Natsu-Mon! 20th Century Summer Vacation, a completely new summer vacation experience developed by the director of the Boku no Natsuyasumi series, Kaz Ayabe, will be released on July 28, 2023, for Nintendo Switch. Publisher Spike Chunsoft also announced that actor Naohito Fujiki will serve as the narrator for the game. A new trailer featuring the game's theme song Funny Bunny, performed by Youko Honna, was also revealed.

In Natsu-Mon! 20th Century Summer Vacation, players can experience various summer activities such as fishing by the river, catching insects, swimming, tree climbing, and more. All of them will be recorded in the player's photo album, and completing the album through these activities is one of the key features of the game.