That was very good. The thing I liked best about it, and all your work, has just become apparent. I was reading a friends LJ post today, a very good fic auther, and they were saying that they only ever write sex scenes because they contain character development.
That's what you're great at. You have the characters down so well, especialy Vash, and your sex scenes are good because they enhance and build those characters. There are pleanty of V/W smut stories out there, but yours are possibly the only ones which are not only completely in-character but serve as vehicles for character interaction and development. That's what makes your work truly special. Really, really brilliant stuff. Hot, highly characterised and very beautifuly written. Great stuff.