^Well, that's kind of the point of them exploring the afterlife.
I have this problem too. I'll have a great plot outlined for the story in general, then put the characters in there and the bastards just run off and do their own thing, or get caught in something else – sometimes really horrible things.
Do you have a trusted reader somewhere?
I found where my last story lurched off into something particularly dark and troubling, I had to send it to a few friends who read a lot of fantasy. They let me know where it needed toning down, where it was okay, and helped me nail the subject matter tactfully.
Characters can be so troublesome and impudent!
I tend to trust my characters. Perhaps that's not always a good idea, I don't know.
After all, I just write the thing.
I've come up with a rather neat idea: that the semi-mythical Sereners in my book are sort of like guardian spirits assigned to a particular person whenever that person is about to die, to sort of 'ease their passing'. But what happens when a Serener falls in love with the person about to die? I'm excited to find out more about them when I fix up the first draft.
Trying to jam characters into plots they would never go for or into things they wouldn't do, seems a sure-fire way to make something bad.
I basically just solved one of the biggest plot holes [that is, why in the world Sereners Yinxi and Na-ah would marry flower maiden Lien; obviously they fell in love when Lien was dying--flower maidens don't live very long]. Now, however, that raises other questions--since Kisa [their daughter] has two Sereners and a flower maiden as parents, what does that make her?