I'm highly doubting that your commission purchaser want any of the backstory depicted in the sexy picture. It just... no.

Lucy/Nyu isn't bipolar, she's split personality, and the one personality is bloody bloody murder all the time. With extra blood. Sexy pictures of them together isn't in character at all, anyway.

The only thing I can actually think of that might make an interesting yuri picture is the fact that they both have these mostly invisible hands coming out of their backs... extra hands could be useful, yes?