Duncan likes traveling as then you exerience new sights, food, and people. Though appears human he enjoys the company of females of almost every race or origin. Interests are varied and if curious you could simply ask.

Does not wish to drink or draw blood, Death is not a turn-on. No biological functions going awry, that's foul.
no surprise switch or fiend packages, won't negotiate gifts for sex  

Not too public

That leaves a lot; especially like elf, hin, mythical, or animalistic if she got the female form.  Walk up, tell, lets' RP into the night.