The 'Greatest Treasure of the Universe, the Seven-Colored Diamond' in Heaven has been stolen by the evil demon king. A mission is given to MOMO, the grandson of Momotaro, by the god of Heaven. With the help of his followers—a dog, a monkey, and a pheasant—MOMO storms the demon king's mansion. However, when the battle begins, his companions prove to be utterly useless. What will become of MOMO as he finds himself in a desperate situation?