Gojikanme no Sensou

Overview

For five years, there has been a desperate war against an unknown enemy. The people on the remote island Aoshima hardly know of the terrible conditions on the mainland. But this changes all of a sudden when every friday at the fifth hour, scholars are chosen to fight directly at the frontlines. Both Saku and Miyako are declared unfit for service for undisclosed reasons. However, young Reina, who had just fled Tokyo, is first to be sent to the war zone.

Source: AniList