Kuma is the son of Sayuri Kumai.He's the larger of the group and has blondish looking hair. He's been friends with Shin dating back since grade 5. Like Uchi and the others, he looks up Shin imensely.
Large and tough, Kumai (called "Kuma", or "Bear" by everyone) always seems to be getting into trouble. He's either getting into fights, or being accused of theft, or being attacked by a rival school. Kuma and Shin are best friends. They grew up together, and Kuma calls Shin "Shin-chan". Even Kuma's mother was friends with Kumiko at Yasue's club. He is also the only former student of Yankumi's shown in the drama version's sequel. In the second series he is revealed to be married to the girl he had a crush on in the first season, and in the third season he becomes a father. Throughout the seasons he helps Yakumi when he sees her students getting into some kind of trouble and becomes a mentor to them as well. In each new series of the drama there is always a kid who greatly resembles Kuma in Yankumi's class..
Kuma is being currently raised by his single mother Sayuri. Not much is entirely known about his father. Only that his father apparently ran out on them. According to Kuma, he and his mother are now paying for his debts; could mean he left due to finacial troubles. Due to the recession, Sayuri's previous business as a bar owner hit hard and she had to close it.