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 to distract them while the DATS escaped.
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.
When ElDradimon was brought into the Real World, Marcus and Agumon ran to rescue the giant, but were confronted by Kouki. He became BioDarkdramon to fight ShineGreymon and Marcus in order to bide Kurata more time to activate the Gizumon Javilin to destroy ElDradimon. After a constant struggle, ShineGreymon manages to defeat BioDarkdramon, and Kouki lost all his powers in the process. But unfortunately, Marcus and ShineGreymon were unable to save ElDradimon as he was destroyed by the Gizumon Javelin.
Later in the final episode of Digimon Data Squad, Kouki was last seen riding a motorcycle without a helmet, with Yoshi (now as a police officer) chased him in hot pursuit.
- Kouki's full name is only given in the Digimon Series Memorial Book.
- Unlike his comrades, Kouki didn't redeemed himself in the final episode of the series.