From JShoujo Scans
Chie's been in love with her next door neighbor, Masao, ever since he moved in with his family five years earlier, but he always treats her like he would a younger sister. Masao's younger brother, Yukio, on the other hand has secretly harbored feelings for Chie for almost as long of a time. One day, Masao suddenly announces his engagement to a girl she'd never met. Will this really be the end of her unrequited love?
This was also adapted into an audio recording in the late 80's.