Long time ago, a thriving civilization blessed by the gods was ruined as a result of a perpetual war. Humanity has built a new civilization, which resembles a medieval world. The young swordsman Jan lives In the kingdom of Cordelia. One fine day he and Ortena, the daughter of the High Priest, go on a treasure hunt. When they return, they find the country overrun by monsters; Ortena's father is killed, and the princess of Cordelia has been kidnapped. The two team up with a legendary hero, in order to rescue those who can still be rescued, and fulfill the legacy of the gods...

Ruin: Kami no Isan is an action RPG. The player navigates Jan through top-down towns and hostile areas; the "world map" is not free-roaming, allowing only linear advancement from location to location. Hostile areas are populated by enemies who are visibly walking on screen.