COY stands for Cross Over Yuri. The premise is pretty simple, I have a list I've compiled of over 600 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.
It should be noted that I've never actually watched My-HiME, and the only reference pic I could find of Yayoi Ota was one lo-res pic. I think I got her basic look right, it's a simple design, but somehow she ended up looking a bit too old, here. So did Haruhi, for that matter.
This pic marks the first time that I've drawn an image, inked it, then decided it's crap and started over. That's right, this is a second draft. Now, I'm not terribly happy with how this turned out, but it's a hell of a lot better than the first draft.
This is an example of how using a giant list of characters can turn out interesting combos. Neither of these characters are very prominent in the works in which they appear. Hell, I could only find one pic of Yayoi (and, like, two of Haruhi). If I was doing this series in any other manner, this pairing wouldn't have ever come up. Hell, neither character would have ever come up.