Because Ryo is an original character created for the WonderSwan Digimon games, he doesn't have a specific partner digimon (the player chooses which digimon he will be partnered with). But in Digimon Tamers the series, it was necessary for Ryo to have a partner. It was natural for the popular Cyberdramon to be chosen.
The WonderSwan game development team from Bandai were the ones who suggested that Cyberdramon should be obsessed with seeking out strong opponents to challenge him.
Like Takato and his friends, Ryo and Cyberdramon bio-merge to become Justimon. Justimon is a character unique to Digimon Tamers.
His long flowing red scarf, whipping in the wind, is inspired by 70s action heroes such as Masked Rider.
Mr. Ikkei Seta, who played Justimon in the Japanese version, appears in many comedy animated series. We worked together on a previous series, "Fun Fun Farmacy". I remember being impressed by his wide range of acting, as he took on the heroic roles of Cyberdramon and Justimon.