Yūta Takemoto, Takumi Mayama and Shinobu Morita are three young men who live in the same apartment complex and are students at an art college in Tokyo.
One day, one of the art professors, Shūji Hanamoto, introduces his cousin's daughter, Hagumi Hanamoto, who has come to live with him and is a first year at the art school. Upon introduction, Takemoto and Morita fall in love with her. Morita expresses his love for Hagu in ways that scare her, especially calling Hagu 'mousey' and constantly photographing her, while Takemoto hides his feelings and tries to be a friend to Hagu. Hagu herself, though initially timid and afraid of company, gradually warms up to the three.
美大学生竹本、真山、森田在破旧不堪的公寓中过着贫困而快乐的生活。
一天,花本老师向3人介绍了他堂兄弟的女儿——小巧、惹人爱怜的插班生·叶久美。
看到天真烂漫的叶久美,竹本和森田在一瞬间坠入情网。
单纯得令周围人不耐烦、迟钝的竹本,以及用令人费解的方式让周围人困惑的森田。在完全相反的两人的爱情表现的交错中,森田自不必说,就连竹本甚至是叶久美也都没有察觉到对方的心情,就这样时间在流逝。
另一方面,真山一直对至今追寻因交通事故而亡的丈夫身影的建筑设计师·理花念念不忘。他同时又逐渐察觉到义无反顾爱着自己的同年级学生·山田的心情…。
希望能填补理花心灵空缺的真山、真山的爱成为负担的理花、唯独对喜欢的真山无法表示关心的山田。
以各自感到恋情、苦于思念的2对三角关系为中心,难过而又有些奇妙的“单相思物语”开始缓缓启动。