Both the Umamusume Agnes Digital and her real-life counterpart are called "hentai" ("the hentai one", "the hentai horse", "THE LEGENDARY HENTAI HORSE") because of their atypical talents for many different types of racing distances and environments, as well as their odd schedule of participating in races. The "hentai" here means "deviant" or "atypical", though for the horsegirl this is also fodder for portraying her as a literal pervert (the other meaning of "hentai") stalking the other umagirls. Even canon alludes to this.