This one suddenly breaks away from the BttF parodies and goes for a semi-veiled Baki reference instead. Not familiar with the character and the alternative pronunciation "ruby character" joke used here, so skipping for now.
Author has removed this from the Pixiv comic series collection and renamed the series to "Umamusume x BTTF Manga". So, removing this from the pool here accordingly.
Edit: Oh there's another comic series up now, for this author's Uma 4Komas. This post has been included too, so moving this into a new corresponding pool.