Young Ryota Honma received a mysterious letter and was taken underground by his classmate Toshiro Tsujitani. Through the time machine, he came to the underwater city twenty years later. There, he saw the wonders of the city, such as moving roads, underwater observatories, etc., And also learned the secrets of urban construction. However, he was in danger of being frozen because his identity was discovered, and with the help of Ms. Xia and Dr. Kirby, he was temporarily left as an archaeological specimen. But he was involved in a student's experiment and almost died. After being rescued by Dr. Kirby, Honma discovered that the doctor was Tsujiya. At this time, the undersea city faced threats from conspirators, and Honma was asked to negotiate with the mysterious Toro tribe. What will happen to him in the negotiations? Can an underwater city save the day?
