After stumbling across a haunted go board, Hikaru Shindo discovers that the spirit of a master player named Fujiwara-no-Sai has taken up residence in his consciousness. Sai awakens in Hikaru an untapped genius for the game, and soon the schoolboy is chasing his own dream--defeating the famed go prodigy Akira Toya!

Sai's games on the Internet have Go players around the world guessing his true identify. Among them is Hikaru's rival, Akira, who suspects that Hikaru is hiding behind the screen name "sai." So intense is Akira's interest, in fact, that he skips the first day of his pro exam for a re-match. And on a rainy Sunday, the battle of wills begins anew....