The Rakuga Kingdom, which floats in the sky above Kasukabe, uses free doodles as its main source of energy. However, the Kingdom is now in danger of running out of energy and they launch an attack on Kasukabe on the surface to try and force the creation of more doodles. The Kasukabe Defense Force tries to repel the attack, but they are soon overwhelmed by the powerful army of the Rakuga Kingdom.
Meanwhile, Nohara Shinnosuke, a 5-year-old boy, discovers that he has been chosen as the hero to save the Rakuga Kingdom. He is given the Miracle Crayon, a powerful tool that can bring drawings to life. Along with his friends, the Almost Four Heroes, Shinnosuke sets out to help the Rakuga Kingdom by defeating the invading army and creating more doodles.
As they journey through the strange and wonderful world of the Rakuga Kingdom, Shinnosuke and his team encounter many challenges and obstacles. They discover that the doodles have a weakness - they dissolve upon contact with water. This leads to an exciting climax where the heroes must fight to protect their creations and prevent them from dissolving in the rain.
Ultimately, the team's efforts pay off and they manage to save both Kasukabe and the Rakuga Kingdom. Along the way, they learn valuable lessons about creativity, teamwork, and the power of imagination. The movie is filled with humor, adventure, and heart, making it a must-see for fans of the beloved anime series.