Originally a surgeon, Kaoru and his brother Masato were involved in an accident on a snowy mountain that claimed the life of Masato. Kaoru survived, but his right arm got severe frostbite and had to be amputated and replaced with his brother's arm.
Kino was later one of the people involved in the "Akatsuki" incident, being one of those given the power of Agito by the OverLord of Light. Because Shouichi Tsugami already held the power to become Kamen Rider Agito, Kaoru's powers instead manifested as Another Agito.
With a deteriorated mental state from the accident on the mountain range that was only made worse by the power of Agito within him, Kaoru began to believe that only he could defeat the Lords and attempted to kill Shouichi Tsugami. However, after being defeated by Kamen Rider Exceed Gills Kino began to help the Riders. Kino was later fatally injured in battle against Volucris Falco after performing surgery to remove one of Ericius Liquor's quills from Shouichi's body.