Is it illegal to write an original story with trademarked characters?

I know that it’s illegal to write or use any kind of trademarked characters. But I was wondering is it illegal to..let say..use Disney characters like “Minnie Mouse” and “Mickey Mouse” and turn them human but write a romantic completely different and Original story about them? They obviously wouldn’t live in a magic house but just enough where the reader would know the characters are “Minnie and Mickey” in an alternate universe. I’m not writing about these exact characters but they are also Disney related. So what I mean is would it be illegal to publish a story where people knew where the characters were inspired from but also completely different environment, physical form,and characteristics? If they were to be published. Kinda like fanfics? Help would be appreciated as a new writer.