Kyōsuke Futatsugi is a research scientist and the series' primary antagonist. He was once a research colleague of Yuuki Mikogami, Haruka Mikogami, and Tamotsu Mikogami. Eccentric and heartless, particularly toward animals, Futatsugi believes their inability to communicate negates fair treatment. This conviction drives his cruel experiments on kidnapped exotic animals and pets.

He harbors intense animosity toward Animalians, viewing them not as a distinct species but as mindless animals disguised as humans. A deep-seated grudge against Tamotsu Mikogami fuels him, stemming from an incident 18 years prior: Futatsugi entrusted Tamotsu to deliver an unsigned love letter to Haruka. Tamotsu's subsequent marriage to Haruka cemented Futatsugi's enduring hatred, despite the mistake being his own.

Weaponizing his scientific expertise, Futatsugi transformed Kamihama into a jungle environment and tested gases designed to induce Animalian transformations on the populace. He manipulated Misa Hatori's trust to advance his schemes, positioning himself as the greater-scope villain behind the Animalian Revolution. His antagonism peaks in episode 50 when he wields an ultimate Kirumin compact, triggering his transformation into a tardigrade with a costume form reflecting that microscopic animal.

Following his defeat, every member of the Animalian Revolution abandons his cause and unites against him, leading to his downfall.