Kouki first appeared while Marcus and the others went on their way to the Digital World. He, Nanami, and Ivan fought the DATS and became the Bio-Hybrids. They easily defeated the DAT's partner Digimon, but were stopped by Commander Sampson and Kudamon, who Digivolved to Chirinmon.
Later, Kouki, Nanami, and Ivan survived the battle, and crashed into Cherrymon's place, where he was taking care of injured Digimon. Marcus demanded what they have done with Commander Sampson. Kouki tells Marcus and the others that Commander Sampson was gone, which shocks Marcus, Yoshi and Thomas. Enraged, Marcus attacked Kouki and digivolved Agumon into RizeGreymon and fought the Bio-Hybrids once again. When Marcus, Yoshi, and Thomas, unlocked a hidden power on their Digimon partners, Kouki, Nanami, and Ivan were forced to retreat. Upon being defeated by ShineGreymon, Rosemon, and MirageGaogamon, Kurata upgraded his powers, also including Nanami and Ivan. During the battle at the Sacred City, Marcus Agumon, Keenan, and Falcomon arrived at Kurata's hideout, and Falcomon attacked Kurata, but was punched out of the way by Kouki. While Marcus was attacked by Kouki, Kurata surrounded ElDradimon with space obsilvation devices, sending the giant to the Real World, forcing Marcus and Keenan to follow it. Kouki lost his powers in the end from his battle with Marcus.
- Kouki's full name is only given in the Digimon Series Memorial Book.