An anime adaptation of the Monster Strike mobile game by mixi.

The protagonist, Ren Homura, returns to the town of Kaminohara, where he once lived. But did he really live in this place before? A nagging feeling tugs at his memories. Meanwhile, a strange game is forcefully installed onto his smartphone - a game called Monster Strike. A gauntlet of battles await him. Through the fierce fighting, he pieces together his scattered memories while uncovering the truth of the game. He's supported by his companions: Aoi Mizusawa, Akira Kagetsuki, and Minami Wakaba. Together they take a step into the unknown, unsuspecting of the secrets hidden below the surface...

(Source: Crunchyroll)