Nice game you have here.

I wonder what letter should I choose... but then again, I probably don't want to actually guess right, do I? It would be much more fun to see Aiko loose another body part. So I'll just choose a letter at random and that would be

K

And if there is not such a letter in this world, then... how about cutting a hole in her belly and make a coil or two of intestines hang out?