A member of the Seto Group. Masa is the one who stole Nagasumi's first kiss (he was actually performing CPR, but anyone would use that as an excuse to say they got a kiss from a man as beautiful as him). Nagasumi's mother and father are very attracted to Masa, but he often shoots their love down for he only loves his close friend Mark. He also transfers to Nagasumi's school, becoming his math teacher. He is often seen with his close friend Mark who he is often compared to in terms of beauty. (Source: Wikipedia)
Before Masa lost his memory he was Onii-sama (brother) Shiranui.