Yuumi is a very nice and shy girl from Kouichi's class. She has liked him for more than two years, and Kouichi likes her too but both of them are just too shy to confess to each other. Yuumi doesn't seem to have many friends and she really likes reading books. She is also very helpful and trustworthy. Spoiler 1 (first episodes)
Thanks to Mao, Kouichi and Yuumi start dating and their relationship seems very solid at first. Unfortunately Yuumi has to move because she is switching schools.When she tells him a few months before the actual transfer Kouichi promises her that he will always be by her side and, if necessary, he would find a job to earn money so he can visit her all the time. At the time when Mao is going out with Kai, Kouichi and Yuumi date all the time,going to different places and being happy and enjoying their time together.Spoiler 2
After Mao realizes her feelings to Kouichi and confesses to him, Kouichi is very confused and is unsure what to do. Yuumi starts to have uncertainties because Kouichi seems to think about something all the time and especially when he sees Mao. Yuumi doesn't ask Kouichi anything about that as she sees how his love slowly disappears.