The weird thing about writing asexual characters is that the vast majority of the time, it is completely irrelevant to the story. Unless you're specifically writing about romance and/or sex. Like, I happen to think Jadis is asexual. I have never and will never write her experiencing sexual desire or having sex. But I doubt anyone would pick up on that from my work, because I don't put her into stories where that would ever come up as an issue.

This may be one reason I like action/adventure stories so much, come to think of it. Even if they have a romance subplot, it's never the point of the story. (I am less sure why I enjoy genre romances. I think it's a combination of a guaranteed happy ending and a focus on interpersonal connections and negotiating how to live with another human being -- I always like romances much more when there's a decent cast of supporting characters and both leads have jobs and hobbies and things that don't get forgotten when they start falling in love.)