"Eiga Sumikko Gurashi: Aoi Tsukiyo no Mahō no Ko" is a feature-length anime film based on the popular "Sumikko Gurashi" franchise, which centers on a group of endearing characters living in the corners of everyday life. The story unfolds in a whimsical world where the Sumikko characters—Shirokuma, Penguin?, Tonkatsu, Neko, and Tokage—embark on a magical adventure after discovering a mysterious book in their attic. The book transports them to a fantastical realm known as the Blue Moon World, a place where magic and wonder abound.

In the Blue Moon World, the Sumikko characters encounter a young girl named Nonoko, who is searching for her missing father. Nonoko reveals that her father, a magician, disappeared while trying to protect the world from an impending calamity. The Sumikko group decides to help Nonoko on her quest, navigating through enchanting landscapes and meeting peculiar inhabitants, including a mischievous cat named Chibi and a wise old owl. Along the way, they uncover the truth about the Blue Moon World's magical energy and the role Nonoko's father played in maintaining its balance.

The narrative explores themes of friendship, courage, and the importance of cherishing small, everyday moments. As the Sumikko characters and Nonoko work together to solve puzzles and overcome challenges, they learn to appreciate their unique qualities and the strength they gain from supporting one another. The story culminates in a heartfelt resolution where the characters confront the source of the world's instability, ultimately restoring harmony and ensuring a safe return to their own world. The film maintains a gentle, heartwarming tone throughout, staying true to the charm and simplicity of the "Sumikko Gurashi" series.