Whilst shopping for some flowers in her local market, Tamako Kitashirakawa, the daughter of a mochi shop owner, encounters a peculiar talking bird named Dela Mochimazzi that decides to follow her home. As Tamako and her younger sister Anko go to the public baths later that evening, Dela has Tamako's childhood friend, Mochizō Ōji, take him to the baths as well. As New Year's Eve arrives, with Dela having put on weight after gaining an affection for mochi, Dela almost chokes on a mochi, prompting the neighbourhood to help him out, overlooking Tamako's birthday.

As Valentine's Day approaches, Tamako suggests the shopping district should hold a Valentine campaign. However, Tamako's father, Mamedai, is against the campaign, believing it to be too modernised. As Tamako and Mochizō start shooting a commercial for the shopping district, Tamako's friend, Midori Tokiwa, feels conflicted by feelings she starts having around Tamako. At the screening of the commercial, Dela manages to stand in for the projector by projecting the image through his eyes. When the commercial finishes, Dela shows another video, this time a video message from his home country. As Valentine's Day arrives, Midori comes to terms a little with her feelings.

Deciding his obesity needs to be addressed, Tamako, Choi and the others decide to put Dera on a mochi-free diet until he loses enough weight to fit into a birdhouse Kanna made. In order to keep watch over Dera to make sure noone feeds him, Choi goes to school with Tamako and the others, where she joins in on classes and helps Dera get some much needed exercise, before going to a used clothes store. As Dera shows up the next day with a curiously slim body, Kanna and Midori give Choi a sweater they made for her.