Ryubee uses the Terror Memory and a special Driver to become the Terror Dopant.
Ryubee and his wife were responsible for creating the devices called Gaia Memories, which allow a person to transform into a monster called a Dopant by accessing the memories of the planet. However, the Gaia Memories proved addictive, with prolonged use causing mental damage. They also created the Double Driver and Lost Driver, which allow a user to transform into Kamen Riders with Gaia Memories without the risk of addiction or bodily harm.
His wife, Fumine, left him after the death of their son, Raito. He carried on his research, and distributed Gaia Memories in secret to the people of Fuuto City, to observe their effects on the human body. Each of these Dopants was defeated by Kamen Rider Double, and later Kamen Rider Accel.
After adequate research from his Dopants, and observing Kamen Rider Double, he chose his daughter Wakana, to become one with the Earth's knowledge by way of an event called the Gaia Impact. Before he can do this, he is defeated by Kamen Rider Double and Kamen Rider Accel, and dies as his home burns around him. At the end of the series, his soul appeared in front of Phyllip, alongside other deceased members of Sonozaki Family, to say goodbye to Phyllip before moving on.