A letter comes to the three Kohda sisters in Kamakura, bringing the news of their father's death. A father they hadn't seen since he divorced and left home 15 years ago. Despite feeling indifferent about their father, Yoshino, the middle of the three, and Chika, the youngest, go to Yamagata to attend his funeral on oldest sister Sachi's request. There, they meet Suzu, their young and reliable half sister.
Umimachi Diary won the Excellence Prize for manga at the 2007 Japan Media Arts Festival Awards. It was also nominated for the 1st Manga Taisho, where it came in 3rd place, for the 12th Tezuka Osamu Cultural Prize, where it came in 2nd place, and for the 13th Tezuka Osamu Cultural Prize.