"Last Bible" is a side-game ("gaiden") of Megami Tensei (Megaten) universe. Unlike all other megaten games, "Last Bible" is not set in modern-day or futuristic Japan. On a distant planet, a race resembling humans possess the ability to call upon a power called Gaia. You are a young boy who learns the arts of Gaia. But the land is in danger - an evil force is approaching. Assisted by his friends, the hero has to summon an army of demons and lead them in a war against the evil. Like in all other Megaten games, you can summon demons and fuse them, getting more powerful variants.