Name : Fujiwara
Sai was an expert GO player in his age, Heian. But once upon a day when he was playing GO in the front of the Ookimi (emperor), he's being cheated by his opponent, unfortunately he was the one accused cheating. Afterward, he was feeling so upset, and hopelessly he decided to end his life by committing jusui (suicide by drowning himself to the river).
But his true love into GO and the goal he hasn't achieved (Kami no Itte) made his spirit lived in a GO ban. Hundred years later he met with Torajiro, later known as Honinbou Shuusaku, who continued his obsession. After Shuusaku's death in his age of 34 because of decease, Sai once again lived in the GO ban and wait for someone to see him. After a long long time of waiting, finally he met with Shindou Hikaru who has no interest at all in GO.
Sai's skill is undoubtedly outstanding, he still remember all the paces during his life and the age of Shuusaku. Sai is indeed a very unique guy, sometimes he looks cool and mature, but on the other time he looks even much more childish than Hikaru. Maybe because he was living in ancient time so he always get amazed when he saw TV, computer, vending machine, aquarium, and even an umbrella. I really love the way Obata-sensei drew Sai with his various funny expressions ^o^.