Monster Strike

Ren Homura returns to his hometown of Kaminohara with almost no memory of the years he once spent there. When his repaired smartphone comes back with a mysterious app called Monster Strike already installed, opening it turns a school rooftop into a real battlefield.

Monsters summoned through the game can injure people, and Ren suddenly finds himself forced to fight with Oragon, a tiny dragon whose confidence far exceeds his apparent strength. As Ren meets others connected to Monster Strike, battles begin awakening fragments of his lost past, suggesting that the game’s appearance on his phone was never an accident.