Takuya and Koichi didn't interact much, even after Koichi joined the group, but when Lucemon Chaos Mode scanned Koichi's data, Takuya was furious and he and Koji became Susanoomon to avenge Koichi's demise and destroy Lucemon.
Upon finding out from his grandmother that Koji existed, Kouichi proceeded to somewhat stalk him, as he was very curious as to what kind of person Koji was. But when Koji was chosen to go to the Digital World and Kouichi was left behind, Kouichi began to feel resentment and jealousy, which caused Cherubimon to take him in and transform him into Duskmon.
As Duskmon, there are some significant traits of his fixation that remain. He starts to regain himself when Takuya yells Koji's name, and eventually regains his memories back. However, his anger towards Koji is still manipulated by Cherubimon and it takes a straight-on confrontation from Koji to get Kouichi back to normal.
Once again normal, and now a member of the DigiDestined, Kouichi continues to pursue his goal of finding more about Koji's personality, eventually developing a protective and caring side towards him. This culminates when Kouichi sacrifices himself in the interests of his brother.
Kouichi survives by virtue of not truly being in the Digital World, and eventually he goes to take Koji to see his mother.
Zoe is the first and only person other than Koji who has a full conversation with Koichi just before the IceDevimon attack in Ice Ice Baby. She is also often seen standing or sitting beside him, and in the episode that Crusadermon and Dynasmon appear in, he can be seen holding Zoe's shoulder's to make sure that she is alright after the Royal Knights attack.
|Main characters:||Takuya Kanbara | Koji Minamoto | J.P. Shibayama | Tommy Himi | Zoe Orimoto | Koichi Kimura | Bokomon and Neemon|
|Other characters:||Ten Legendary Warriors | Celestial Digimon | Gotsumon | Sorcermon | Katsuharu, Teppei, Chiaki, Teruo, and Angemon | Other characters|
|Antagonists:||Grumblemon | Ranamon | Arbormon | Mercurymon | Cherubimon | Royal Knights (Dynasmon and Crusadermon) | Lucemon | Murmukusmon and Ornismon|
|Other media:||Island of Lost Digimon | Things That Want To Be Told | A Train Named Hope | Digimon BattleSpirit 2 | Legendary Skies | Force Three | Visual Dictionary | Music | Singles | Albums|
|Relationships:||Takuya Kanbara | Koji Minamoto | J.P. Shibayama | Tommy Himi | Zoe Orimoto | Koichi Kimura|
|See also:||Digimon | Digital World | DigiDestined | D-Tector | Spirits | Fractal Code | Holy Ring | Digi-Egg | List of episodes|