Period: Cube ~Shackles of Amadeus~

Searching for clues about your missing brother, you and your childhood friend Hiroya begin playing an online RPG called “Arcadia.”

You’re suddenly enveloped in a flash of light, and awaken to find yourself in a mysterious fantasy world. You discover you’ve been sent inside of the game, and learn that the only way out is to complete it. In a deadly world on the verge of collapse, you become the “Almighty,” the key to clearing Arcadia, and the secret weapon everyone is after.

You and your companions undertake a perilous journey, where love grows as the world falls apart.

[From the official site]