At episode 7, he apears as Keitaro Urashima's rival for Naru Narusegawa's affection, but winds up failing and gives up. In episode 11, he becomes Naru's manager when she becomes the Hinata Idol. When Naru runs away, he hires Motoko Aoyama and Shinobu Maehara as his second act " Sword and Flower " - and they become popular too. However, itsune Konno 's mismanagement of the company's funds run it into bankruptcy and Kentaro has to work for Haruka Urashima to pay off his debts for the rest of the series.
Despite the fact he's broke, somehow he's able to afford a sports car which is seen in episode 25, the Christmas special and Love Hina Again. Also he somehow had money for a mechanical flying drill in the Spring Special. Go figure.
In Love Hina Again, he helps Keitaro by providing keys to the Annex - at great peril, for Haruka would get volently angry at him when she found out.
He started out as an rival and possible enemy of Keitaro Urashima, but at the end of the series, he wound up being a friend to Keitaro.