Wataru, a boy in grade four, gets blown into a world in another dimension, Shinbukai, where he is told he is the hero of this world. He becomes able to summon Ryujinmaru, a robot-like partner, and he helps save the people of the world from an emerging evil power.

The other-dimensional world where Wataru had secured peace is in danger of occupation again. Wataru is back with an upgraded Ryujinmaru to stop Dowarudar, the evil of all evils.

Wataru, a fourth grader, is once again taken to Shinbukai, a world in another dimension, as its savior, ten days after he had last returned from there. He heads for the Soukaizan, invaded by the Donarukami family from the dark world. Wataru enters the Soukaizan with Himiko and Shibaraku. As they meet new friends along the way, they also bravely confront their enemies. Will Wataru be able to stop the Donarukami’s plot?