Okay, I've spent about 30 minutes on it, I think. Here is what I have so far:
If you like it how it is tell me, but I'm not working on it anymore until you tell me there is a problem with it.
I went with the dark style because both of those characters are dark to me and I thought that since you chose those characters that you'd like a dark look. It just seriously felt wrong to try to make it look cute. lol I hope you like what I have made so far. I tried to add as much as I could without distorting the characters too much. But I also realized that you'll expect to find more stuff on there than just the two characters. I think it has 18 layers in PSD format (including the hidden flames, Japanese, two characters, hidden red airbrush stuff, the white overlay line, and the username layer) and if you see something you don't like, just tell me. I can remove it for you. Just so you know, all that Japanese junk means "heat", and "pain and suffering."
PS: Don't ask me to make it bigger. I don't make sigs much bigger than it is. It's on the standard 400x100. I don't know how big my sig is.