Depending on the adult manga by Miyabi Tsuzuru.

It's time for your local summer festival and Kentarou is accompanying Shizue, who's arrive at visit after being away for a few years. During the festival Kentarou leaves Shizue alone for a bit, and when he finds her again he sees a surprising scene...

Later, Shizue travels to an area photo studio to get a few photos from your summer festival, and decides to do a bit of modeling while there. In a short time Kentarou also joins...