Smut fiction is a type of fictional writing that contains sexually explicit content. It often focuses on sexual encounters, relationships, and desires. However, it is considered a form of adult - oriented literature and may not be suitable for all audiences.
Well, a smut novel refers to a book where the focus is heavily on sexual themes and often has very detailed and graphic descriptions of sexual acts. It's not for everyone and is usually considered more adult-oriented.
It could be a new character created specifically for this fanfiction. Maybe a young inventor or scientist who idolizes Tony Stark so much that they seem to be at his every beck and call, giving the impression of being 'leashed' in a sense.