Оґата Сейджі

A Go professional 9-dan and student of Touya Kouyo. He first took notice of Hikaru when the latter explained a go move during a children's tournament that even professional Go players would take some time to see (which was actually Sai's doing) and later, as the rivalry between Hikaru and Akira emerged, catalyzed its development for several times, such as helping Hikaru to be accepted into the Insei test and occasionally reporting Hikaru's progress to an uninterested and disillusioned Akira. After the Net game between Touya Kouyo and Sai, Ogata also became obsessed with playing Sai and constantly nagged Hikaru.

Unbeknownst to him, his request was finally granted just before Sai disappeared, during a game with Hikaru when he was too drunk to notice Sai was playing.

Ogata is one of the best young Go pros of Japan, having been the challenger for many titles throughout the series and finally winning the Gosei and Judan titles when Touya Kouyo retires. He's frequently after the Honinbo title Kuwabara currently holds and this sparks a rivalry between them.