An 11-year-old American university graduate, who befriends Akira. He is rich and lives in a huge mansion. He is the successor to the Kujou family, known for its experimentation of daemonic experiments using traditional techniques of yin and yang. To atone for his ancestors' sins, Haruka volunteers to fight the Kokuchi alongside Akira, despite him not being able to physically fight them.

He develops a close connection with Kou in the anime and the elder persuades Haruka to call him "Onii-chan" shortly after they meet.

He uses a crossbow. Haruka was created specifically for the anime and does not appear in the manga.