In the city of Kasukabe, a newly elected mayor named Mamoru Shizime launches an aggressive environmental initiative called the "Human Animalization Plan," aiming to combat ecological destruction by transforming humans into animals. However, this plan takes a dark turn when Shinnosuke Nohara, along with his family and friends, unknowingly stumble upon a mysterious small bottle containing a light green liquid while cleaning the riverbank. Curious, Shinnoseke brings it home, and during the night, his parents, Hiroshi Nohara and Misae Nohara, mistakenly consume the drink, which begins their transformation into animals—Hiroshi into a rooster and Misae into a leopardess, or jaguar.
This bizarre transformation sets off a chain of events that threaten the entire city. When friends visit the Nohara family, a menacing group led by a figure named Bunbetsu appears, attempting to capture them but initially failing. Help arrives in the form of Victoria, a mysterious woman who assists the family in escaping, but their troubles are far from over. Eventually, due to a misstep—where Hiroshi, now a rooster, leads them to a false path—the group gets caught and stands before Mamoru Shizime himself. It turns out that the drink they ingested is the "Human Animalization drink", a product of Mamoru's plan designed to eradicate ecological harm by transforming humans into animals. Tragically, once someone drinks this potion and transforms into an animal, all memories of their human life are erased forever.
As the story unfolds, Shinnosuke, his friends from the Kasukabe Defense Force, Himawari Nohara, and Victoria make a daring escape. However, Hiroshi and Misae are taken away on an airship, leaving Shinnosuke and his companions to plot their next move. Just before leaving, the group—composed of humans with animal parts (like bats, penguins, rabbits, and pangolins)—sets out to find Bumbetsu and uncovers an underground forest with a hidden base. Using their animal powers, they attempt to thwart the villains’ plans but are ultimately captured again, leading to a confrontation with Shinnosuke’s fully transformed parents.
In a heartfelt and intense showdown, Misae, now a leopardess, regains her memories and escapes, freeing the Kasukabe Defense Force to use animal powers against Mamoru's operatives. Meanwhile, Victoria, who reveals herself to be Yoshiko Shizime—Mamoru’s wife—enters the fray and destroys the base from within. As the drainage systems are dismantled, Hiroshi and Misae finally recover their memories, bringing relief to Shinnosuke and his family. Yet, the chaos isn’t over, as the entire city of Kasukabe begins transforming into animals due to Mamoru’s ongoing execution of the plan.
Ultimately, a monument emerges from the underground, signaling the final confrontation. Mamoru Shizime transforms into a Chimera after consuming a special potion called DX, and the battle reaches its peak. Shinnosuke, transformed into an elephant but too small to effectively fight, is aided by Himawari, who becomes a polar bear and helps turn the tide. During the clash, Yoshiko reveals her true identity and explains that Mamoru’s radical plan was driven not only by his despair over environmental neglect but also by his love for her, as she herself didn’t care much for nature either. Mamoru, overwhelmed with love, decided to smash the animalization potion—a decision that helps reconcile their relationship.
With the conflicts resolved, the animalized humans are reverted to their original forms, and the city of Kasukabe returns to normal. Hiroshi, now more environmentally conscious than ever, embraces a renewed outlook on protecting nature, and the peaceful daily life resumes. This story, blending comedy, adventure, and a heartfelt message about ecological responsibility, underscores the importance of caring for the environment and the power of love and reconciliation in overcoming even the most seemingly insurmountable challenges.
