Yuusaku Godai's steady date and generally serves as an obstacle for him in his pursuit of Kyoko. Cute, sweet, and a little scatter-brained, she's oblivious to the fact that she is more interested in Yusaku than he is in her, and she does not recognize Kyoko (or later, Ibuki) as competition for his affection. Their relationship starts after Kozue finds Yusaku with a spare movie ticket (originally intended for Kyoko, who had just started dating Shun) and she invites herself along, setting the general tone for their relationship. Yusaku would like to come forward and break things off with Kozue; however, he either cannot find the right opportunity to do so without hurting Kozue's feelings deeply (Yusaku's view) or he is unwilling to "be a man" and stand up for himself (Kyoko's view). The situation becomes more complicated after Kozue introduces Yusaku to her family (Yusaku did not know Kozue's plan until they had already arrived at her home), who approve of him and are all too willing to feed the perpetually starving college student.

Kyoko does not dislike Kozue and always responds to Kozue's genuine friendliness in kind, but Kozue's relationship with Yusaku does trigger her jealousy (which she would not admit as such) and as a result he always takes pains to keep all mention of Kozue away from Kyoko. Yusaku does find Kozue attractive, and admits to himself that he would have fallen for her if Kyoko was not in the picture, but because of his feelings for Kyoko he strives to maintain some sort of distance from Kozue; his naivety (both feigned and genuine) keeps their relationship platonic.

Another running gag in the series is Yusaku's many attempts to break off with his relationship with Kozue. He imagines putting himself in many degrading situations to make her hate him and break up with him. Ironically, this does happen when Kozue sees Yusaku escorting a very drunk Akemi out of a hotel although it was not Yusaku's intention at the time.

Later on, she finds out what really happened and the two of them part ways peacefully. Kozue ends up marrying a co-worker, Kentarou, at the bank she works at and moves away to Nagoya with her new husband.
(Source: Maison Ikkoku Wiki)