Sai Fujiwara is the spirit that inhabits Hikaru Shindou in the hit anime and manga series Hikaru no Go. When alive, Sai was a GO teacher at the Heian court. In a game before the Emperor, his opponent cheated, and thenproceeded to accuse Sai of cheating. When ordered to continue the game, Sai was totally distraught by the dishonesty of his opponent, lost his concentration, and lost. In his shame, he commited suicide by drowning himself.
However, his ghost was not able to rest, and inhabited an old Go board. Throughout history, he inhibited various famous Go players, the most famous being Honinbou Shusaku. Being one of the greatest Go players of all time, his hosts could not help but learn from him, and make Go history for themselves.
And now, he is within Hikaru,a friend,sometimes annoying, but always willing to give his advise, and play Go with Hikaru, thereby teaching him to play. And slowly, Hikaru's skill begins to match Sai's, and so... (The rest would be spoiling)!
PS.: Yes, although he is designed with long hair, and fine faetures, he is most definitely male. | 
