I'm actually not sure if that is really an alternate-color Eirin or just a look-a-like. On pixiv it's tagged with Aki_Minoriko, but I'm pretty sure that's not supposed to be her. I could be wrong, though.

Minoriko was shown in the previous page, and Yorihime is shouting "秋穣子だ!!" (it's Minoriko Aki!!) but it's likely just Yorihime mistaking her identity in a stony-faced goof, if i had to guess.

I can't tell for sure without translation but without checking back too many pages, Eirin (or some form of her?) seems a safe bet at least for now.

I went ahead and put this in the Scarlet Devil End of Digression pool even though there are some pages missing in between the last uploaded page and this one. I wish there was more interest in translating Potato Pot's stuff!