Theatrical follow-up to the second season Kobayashi-san Chi no Maidragon S and Kobayashi-san Chi no Maidragon S: Nippon no Omotenashi (Attend wa Dragon desu) OVA. 

"I don’t want to let go of her hand. Because, we are a family."
 
Miss Kobayashi, Tohru, Kanna, and Iruru's peaceful lives are shattered when Kanna’s father, Kamun Kamui, leader of the Chaos Forces, arrives and forces her to return to the Dragon World to fix a past mistake. With a war brewing between Chaos and Harmony, Kanna must find a way to unite the two worlds but is torn between her loyalty to her friends and her father's demands. Miss Kobayashi, however, refuses to let her go and tries to mend Kanna and Kamui’s broken bond. As dragons clash, Iruru uncovers a hidden force manipulating the war. Can they stop the war before it consumes both worlds?
 
(Source: Kyoto Animation YouTube Channel, Crunchyroll)