Rei is a teen-aged boy with pale skin, gray-green hair and red eyes. He wears a black hooded jacket over a gray hooded sweatshirt. He also wears dark blue pants with a white zipper pattern, and white sneakers.
- Rei Katsura (桂 レイ)
- Ja: Katsura (桂?). Japanese surname that means "Cercidiphyllum japonicum". Might also refer to the Katsura River or Katsurazawa Dam as a reference to the Net Ocean.
- Ja: Rei (レイ?). A Japanese gender-neutral name. Possibly from Ray Kurzweil (レイ・カーツワイル Rei Kātsuwairu?), author of The Singularity Is Near. It also means "zero" (零 rei?), and with Hajime is a pun on "01".
Rei is an Appli Driver paired with Hackmon. He is aware of Haru Shinkai's existence. Soon after Haru and Gatchmon collect their first 7code Appmon Chip with Ropuremon, Rei and Hackmon obtain their own when they defeat a cornered Mailmon. Hackmon comments that Haru has obtained his first 7code Appmon, and Rei says that he "couldn't" allow Haru to reach Leviathan. On November 3, 2016, he sees Eri Karan and Dokamon on television and declares that things are getting interesting.