This is a long shot, because I really don't remember much of it and it's been several years since I've read it. As far as I'm aware, you could only access it through the web. They might have changed it since then, though. I think it's probably classified as more of a vampire romance type of VN. The main character centered around a boy who turned into a girl (I really can't remember why, I just remember they started out as a boy and ended up a girl) and they met a vampire who, if I'm remembering correctly, turned out to be a Prince. But it was set in a (somewhat) modern time. I remember the boy/girl going to school.
Anyways, I know it isn't much to go on, but that's all I remember. It's been like five years since I've read it, I'm sure. If you know of anything that sounds like this, please let me know! Also it was written in English. Or the version I read was written in English, at least. Thanks for any help.