Card Captor said
I was under the assumption that I would be required to play the new husband, so I'm fine with that. As for story elements and such...well I think the setting is something that needs to be established first; What time period does it take place in? What's the level of technology? Is there magic if so, how advanced is it and what is it like? Are demons common knowledge? I'm honestly not too picky about any of these, but you might be. These are things I like to get established before working on the plot of an RP
Well being a husband is one thing; but he very much could of had a life before hand so I suppose the better question is "what kind of character do you want the husband to be" would be a better answer. - As for era that is entirely open for adjustment; but keep in mind I don't really care for modern themes. Though the fact that it's an arranged marriage should be a hint of how far back it may or may not be. - If you like demons can be common knowledge - however it would be clear that the demoness in question has fooled the human's family into believing she was human.
The only other thing I could see needing to be ironed out is exactly why she choose him. which would be entirely up to you.