Mugetsu and Gengetsu are the two Extra-stage bosses from the Touhou game Lotus Land Story, which was notable for introducing Kazami Yuuka. They're also sisters.
Typesetter here. Since DynastyScans is rather slow in accepting requests, if you want to see more of these, here's an imgur album of Hachiko's comics that I typesetted (updates daily).
Kogasa is a popular ship with any character, it seems. Seems odd, but it feels like she's become the breakout character of UFO, even Hijiri has a hard time keeping up.