Santa Company is a worldwide organization dedicated to delivering presents to children. Santa Company's elves—known as "tonttus"—aid several Santas every year by wrapping presents, raising reindeer, and helping with deliveries. Mint Rondo is one of the many new tonttus arriving at Santa Company's tropical island office. Following in her older brother's footsteps, Mint begins training alongside her friend, Thomas Dou, and rival, Noah, to eventually become a Santa herself. Unfortunately, her clumsiness causes her to fall far behind her peers and into her brother's shadow.

One day, while sitting on the beach, Mint, Thomas, and Noah discover the biggest threat that Santa Company has faced yet: ocean pollution! With the accumulation of litter going unnoticed, the growing hazard will soon endanger the surrounding ocean wildlife and the members of the Santa Company. As trouble looms over the horizon, Mint might just be able to clean up her act and save everyone on the island in time for Christmas Eve.

Santa Company: Manatsu no Merry Christmas was produced in conjunction with the Nippon Foundation's "Change for the Blue" initiative in order to raise awareness about ocean pollution as part of the Umi-to-Nippon project. The film made its worldwide debut through MyAnimeList on January 28, 2021.

It is an original work brought to life by Kenji Itoso. A short animation was released in 2014 after a successful crowdfunding campaign, followed by a feature-length version released in Japan in 2019. This work is a spin-off featuring some of the same characters.