When the monster Dopants, who use the power of the Gaia Memory, begin to operate in the windy city of Fuuto, the young Shotaro becomes an assistant to the detective Narumi Soukichi and spends his days chasing after him. Shotaro, who knows nothing about Soukichi, who secretly works as Kamen Rider Skull in addition to his detective work, becomes increasingly frustrated. One day, a new request comes into the Narumi Detective Agency, leading Shotaro and his team to a fateful night.