Kazama Shoto's actual partner Digimon is Zephagamon, but he used MedievalDukemon in the Digimon Liberator webcomic.
The other illustrated "Digimon" in the back is Mother D-Reaper from Digimon Tamers, who has a card in the Digimon Card Game, which has a really high DP count and is unaffected by any effects of the opponent, but cannot attack at all.
A certain Shoto card (EX7-064) gives your own Digimon some keywords, the important one being blocker and combined with Mother D-Reaper, it gives you a low cost, high DP blocker consistently, which cannot be interacted with.