Professor Katsumi, the narrator, a computer scientist. Committed to rational explanations, Katsumi comes to see that his own future is not easily controllable. When he builds a computer that will predict the future, he becomes involved in the murder of the man whose future he is predicting. Eventually, Katsumi discovers that the victim had learned of a bizarre project to develop aquans, a race of fishlike humans who could survive the predicted flooding of Earth. Katsumi discovers that his own staff, guided by his computer, are participants in the project. He confronts the computer, and it explains that, as his second self, with an insight into the future that he refuses to accept, it is in control, not him. Because of his objections, Katsumi must be killed.
Tanomogi, Katsumi’s assistant. Although the mysterious Tanomogi seems to be helping Katsumi, he has been manipulating his boss. Tanomogi is the murderer that he and Katsumi have been seeking. He feeds Katsumi information about the aquans, but he never specifies his motives for joining the project.
Wada Katsuko, a young female assistant. At times strangely attractive to Katsumi, Wada is the link between the aquan project and the computer laboratory. She also arranges to procure Katsumi’s aborted son for the project so that Katsumi can have a part in the future society. Later, she tries to convince Katsumi that he is responsible for the consequences of his actions.
Professor Yamamoto, the head of the aquan breeding facilities. A large, businesslike scientist, Yamamoto dispassionately explains the project and its aims to Katsumi shortly before Katsumi is to be killed.