Digimon Partner to Ichijouji Ken
Wormmon starts out as Ken's digimon, though the relationship is pretty rough at first. Ken treats him poorly, and Wormmon just takes it—he's loyal to a fault. But as Ken's character develops and he stops being such a jerk, their dynamic completely changes. By the end of the series, Wormmon becomes a genuine friend and partner to Ken and the rest of the group, working alongside all the other kids and their digimon. It's one of the more satisfying character arcs in the franchise, honestly.
Content compiled by AnimeList.moe from publicly available sources.