Sagashi Mono wa, Natsu Desu Ka.

Kyouhei Utsugi, the main character, returns to Amakawa Town for the first time in years.
At the candy shop he used to visit as a kid, he meets a strange girl named Makoto Orihara and gets roped into helping her look for marbles.
Meanwhile, girls have started disappearing in Amakawa Town, and rumors of "spirited away" incidents are spreading.
Hearing these rumors brings back memories for Kyouhei—he remembers seeing a girl disappear right before his eyes when he was little.
What is she really searching for? What’s behind all these disappearances? Where did that girl from his memory go? All these mysteries start to overlap.
A slightly bittersweet boy-meets-girl story set over one summer.

[Translated from Steam]