Six years ago, a massive explosion occurred in the town of Ouma, but miraculously, there were no fatalities.

In this town, where a mysterious sphere called "Glass Sun" floats in the sky, a boy named Kagari Mera, who feels out of place and lives a boring life, meets a mysterious girl named Thirteen on his 16th birthday.

His encounter with her brings vibrant color to Mera's previously monochrome life, but at the same time, strange occurrences begin to happen in the town.
(Source: Official Site, translated)