Megami Tensei Gaiden: Last Bible is a role-playing game for the Game Boy and the first entry in the Last Bible series, created as a spin-off of Megami Tensei. It follows a young seeker of the power known as Gaia who travels with two companions to investigate beasts that have begun appearing from the sky and attacking people. Gameplay consists of exploring fields and towns, managing equipment and magic, and fighting command-based battles. The party can include the protagonist, two human companions, and up to three recruited beasts. During encounters, beasts can be negotiated with and recruited as allies, while recruited beasts can be fused to create new creatures. Human characters gain experience and levels, and the player can improve selected attributes as they progress.