Ume harbors a secret crush on her classmate, Isezaki-kun, who she believes to be happily taken. Instead of chasing him, she chooses to observe him from afar and writes her observations in a little notebook. However, one day, Isezaki asks to borrow her class notes… only for Ume to accidentally hand him her Isezaki Observation Diary! Isezaki takes the mistake in good humor, but soon rumours begin to float around the school of Isezaki breaking up with his girlfriend? Could this be Ume’s big chance?