I've been following this manga for over 6 years now, but it wasn't until I translated these extras that I learned of Nakai Akira's existence. I went back to double-check and found that she appears in chapters 22, 69, and 72. She even makes a brief appearance in episode 6 of the anime.
Another hidden yuri couple... makes sense, makes sense.
Though considering nekotoufu's like of writing yuri doujins, I've been expecting a bit more overt yuri than just the few glimpses and onesided jealousy we've seen throughout the series so far.