The time left is only one night. Save the world with the power hidden in 12 types of GEM. "12GEMs" is an RPG that uses the power hidden in 12 types of GEMs (jewels) and travels while summoning partners sealed in each GEM. The beginning of the story is the aerial castle "Ganseld" floating in the sky with the power of GEM. The people living in Ganseld chose themselves as noble people, and the lower world on earth was taught as a place where unclean people and horrible monsters wandered around, and they lived without involvement. However, one day, the GEM that supported Ganseld suddenly scattered to the uncurled ground. In order to prevent the castle from falling, the main character, the boy "Dino", received the order of collecting GEM and went to the lower world, but it was a mysterious and mysterious world that was different from what was taught in Ganzeldo ... Until Ganzeld crashed, there was only one night left. The fate of the world was entrusted to a boy.