COY stands for Cross Over Yuri. The premise is pretty simple, I have a list I've compiled of over 500 cute girls from various anime and manga. I then use a random number generator to make pairing, which I then draw. Every third picture is a threesome.
So here's the third COY pic. While I'm very happy with how Tenma and Euphie turned out, Guu's face and body overall have always bothered me. I imagine if I were to draw it again today it would be a bit better, but I'm not as attached to this pairing as I was the last two COYs. Still, I suppose it's a mark in my evolution as an artist, lol.