With the collapse of ZAIA Enterprise Japan, Gai Amatsu establishes a new company with a secretary-type Humagear Rin. But something went wrong with his body, and Kuroto Dan appeared and separated from his body! The Bugster Virus, which was wandering in the internet and was revived by Ark and infected Gai! Gai transforms into Kamen Rider Tho to try and get rid of the virus, but Tho looks black for some reason.