Epona is a villainess from Ys Origin.
Epona is a member of the Clan of Darkness who serves Dalles, along with her brother Kishgal. She doesn't seem to have any real objective, merely following her orders and never bothering with the details. She's ordered to find the twin goddesses on Darm Tower and to stop the knights sent from Ys to find them, which leads her to confront both Yunica Tovah and Hugo Fact.
In Yunica's story Epona barely acknowledges her, initially summoning a demon to keep Yunica busy and then leaving. Only after Yunica defeats her the first time does she shows some respect to her opponent. She is confronted later again, ending knocked unconscious. In Hugo's story Epona is initially annoyed at Hugo's cocky attitude and decides to confront him, but ends defeated. She attempts to fight him again by summoning two demons, but they turn on her, forcing her to ask for Hugo's help. After being saved she starts to like Hugo, trailing him and saving him when he attempts to blast the demonic door on Rado's Annex. When Hugo loses control over the demonic essence given to him by Dalles, she snaps him out of it, but Dalles casts a petrification spell on her for betraying him, which slowly turns her to stone and makes her crumble into dust on Hugo's arms. In Toal Fact's story (the canon story), Toal saves her when Hugo cokes her while under the demonic essence's influence. When Hugo comes to his senses, he takes Epona away to recover while Toal goes after Dalles. In the end Hugo reveals Epona survived and went back to her country.