Gai Amatsu is a central antagonist in the tokusatsu series Kamen Rider Zero-One. As the CEO of ZAIA Enterprise Japan, he is highly intelligent, manipulative, and driven by a desire for technological dominance. Gai transforms into Kamen Rider Thouser using the Thouser Driver and Zetsumerise and Progrise Keys. His role is to challenge and undermine Hiden Intelligence, orchestrating schemes to seize power and defeat the main protagonist, Aruto Hiden. His ruthless tactics make him a formidable adversary.