Monster Strike: Deadverse Reloaded

Ren Homura returns to Kaminohara, but his memories of the place are hazy. Upon collecting his repaired phone, he finds a mysterious game called Monster Strike installed on it. Ren opens the game, unaware of its purpose, and is suddenly attacked by a stranger.

This encounter occurs on the roof of Ren's school, now designated as a "stage," where the stranger summons a realistic monster from the game. Ren tries to summon Oragon, the dragon he was told would save him, but it's a small and useless beast.