ワルキューレのキコ

Valkyrie no Kiko

In the manga's story, humanity fought against divine beings in a secret war for its existence seven years ago. A girl named Waka, as well as her companions became Valkyries chosen by the gods and gave their lives to end the battle. In time, Waka's younger sister Kiko grows up and enters high school. But now the divine beings have returned. (Source: Anime News Network)