Ryuo and the princess of the Dragon Palace of the sea to spend peacefully in the beautiful Dragon's Palace floating in the rich sea. On the other hand, in another sea area, new kingdom made of plastic caused by marine pollution was born. Monsters which mixed gather, and King plastic of the leader bears a grudge for human being and other creatures, and have there a lot of thing thrown away as garbage and creatures which lost hope; paid more attention.
One day plastic King begins sudden attack in order to obtain the Dragon's Palace in a large flock with subordinate. While dragon king of the sea is arrested, and the princess of the Dragon Palace that ran away by a hairbreadth transforms itself into tortoise, and we are chased by plastic monster, we leave for bank. We were saved then by boy, Taro of one whom we approached by the sea.
The Dragon's Palace which was attacked by plastic monster of plastic King and subordinate. Therefore we save people living in Ryuo and family, Palace of the Dragon King of the sea becoming the body of falling into enemy hands, and the princess of the Dragon Palace that wants to regain the Dragon's Palace appears for odyssey with Taro. Travel must find legendary tool to make possible in the Dragon's Palace followed in intense ocean current to change every season in space-time, at first, to be called Urashima's box to come back.
According to the old tale concerning place of Fukuoka, it is said that Urashima's box is enshrined in "ancient shrine" in island across the sea. Plastic monster of pursuer approaches to catch princess of the Dragon Palace and Taro toward island hastily. Two people who obtained Urashima's box safely passed through warp tunnel which Urashima's box produced and arrived at town of summer Fukuoka across space-time.