Cursed by the gods, on the verge of death, the protagonist of the game is transferred to a different realm - a fantasy land ruled by sword and sorcery, in which humans are threatened by rampaging goblins, orcs, and a mysterious dragon. The hero must find a powerful artifact known as the Heart of Phantasm in order to return home.

Mugen no Shinzō is a role-playing game similar to early Ultima games. The player controls a lone character with basic attributes who roams the vast land, visiting towns and dungeons. Overworld navigation is done by scrolling with arrow keys, without an icon to represent the player character. Town locations have little to no graphics; along with the dungeons, they are displayed in small windows. The maze-like dungeons are represented by abstract pseudo-3D vector graphics. Combat is random; the protagonist fights enemies one-on-one in simple turn-based fashion.