He is a children's author who has gained commercial success for his book The Girl and the Dollhouse which he wrote to reflect his feelings for his daughter Rikako who died several months ago. He uses the Puppeteer Dopant's power to take revenge against those who give his book harsh criticism by controlling his daughter's doll, Riko, as the instrument of his vengeance. He particularally seeks revenge against those who claim he did not truly love his daughter.
After being exposed, getting a new puppet in Wakana Sonozaki by Shinkuro Isaka, Horinouchi turns his attention towards Akiko Narumi before being defeated by Kamen Rider Double CycloneMetal's Metal Twister Maximum Drive.
- Height: 195 cm
- Weight: 98 kg
As the Puppeteer Dopant, he uses special puppet strings to take control of whatever he wishes and carries a flute that produces super-sonic waves.