First thing I noticed about this was Litchi. The pose, body language and all around expression just spell out sexy. That's especially important considering the character you're telling us about. Anybody that doesn't know BlazBlue could safely assume she's a femme fatale with a bit of class.

As for Taokaka, the flailing sleeves and kicking legs help give a wild side to the picture. She has a lot of motion and that crazy grin under her hood are a good contrast to Litchi's calm. So as far as composition and ideas for this piece goe, I think you nailed it. The two play off each other well here.

As for technique, there's a lot going for you here too. There's a fine balance of light and shadows, giving the picture a strong moonlight glow. For every bright part there's a deep dark part to balance it out. And that swirl affect on Litchi's hair looks great. It adds some good motion to an otherwise still pose.

Now to point out a few details that could help make this piece even better, or to focus on for next time:
Litchi's skin looks great- smooth and sexy, just how it should be for a character of this type. I'm digging those shoulders, among other things. But her left shin looks a bit "streaky", like it hasn't been blended like everything else. Also, that leg seems rather straight on your left side. I imagine someone of her figure would have slender legs; they'd smoothly taper off more as we get closer to the ankle.

I didn't notice this at first, but it seems like Litchi doesn't have much of a neck. It could be because her shoulders are shrugged and her head is tilted a bit. But, I tried picturing it here if her head was up straight, and it would still seem rather stubby. This could be a tricky one to fix, so just double check next time. A lovely lady like this deserves a nice neck to go with those shoulders and face, after all.

So I found a couple details to nitpick on, but as a whole, it's another brilliant work, Hoshi sempai. It makes me excited for BlazBlue's release in the States, so that shows it's an excellent fan work. You gave the characters plenty of appeal and the background and scenery top everything off with some firm substance. Keep up the good work!