Another insei friendly with Hikaru, he appears to be doing very well in the first pro exam shown in the manga, going undefeated, until his match with Hikaru. During that match, rumors about Hikaru's incredible strength add to the pressure of time constraints, and as a result, he misplaces a stone; his attempt to move the stone after letting go of it ends up with his resignation before Hikaru can accuse him of cheating. As a result, he is defeated in his next two games and loses his chance to become a pro. He later learns to control his emotions and passes the next year's pro exam without a single loss. Isumi also unknowingly helps Hikaru get over his loss of Sai when their practice game makes Hikaru realize that by playing, he can find Sai within his moves, the Go that Sai passed on to Hikaru. Isumi's birthday is April 18th.