Summarized From "VNDB":[https://vndb.org/v11643]:
It's summer vacation! It's time for free study but Koudai and three girls in his class aren't sure what theme to make for their summer study. Koudai has a map he found at his grandfather's home listing the location of treasures. If you collect all the treasures, you get to make a wish! But there's a catch. You need to search for the treasures naked!
let's la go! bokura no jiyuu kenkyuu