Original skeb page reveals that it's the commissioner's OC, as well as another OC (presumably an acquaitance): https://skeb.jp/@kou_hiyoyo/works/2079

Jnglmpera said:

Original skeb page reveals that it's the commissioner's OC, as well as another OC (presumably an acquaitance): https://skeb.jp/@kou_hiyoyo/works/2079

Ardan and Dober Blanche Luna and Amakakeru Tsubasa, both completely original OCs not based on any IRL horses. Luna (the one on the left) in particular gets drawn by quite a few different artists and even has a Pixiv tag. That said most of her art seem to be from the one who came up with the OC (usernamed Montbretia) commissioning those artists to draw his OC.