TW: grooming
Wife Husbandry is different than just an age-gap romance, and it’s usually not considered incest, either.
The Wife Husbandry trope involves an older, handsome, protective male lead who is not blood related to the FL. He swoops in to start raising the FL, often becoming a legal guardian.
The female lead generally falls in love first. She desperately wants to be viewed as a woman and treated like an adult by the ML. She has zero familial support (either she's an orphan, her parents abandoned her, etc.). and is typically in high school.
All three that I mentioned (wife husbandry, age gap, incest) would fall under the “taboo relationship” or “forbidden love” category, which I enjoy reading. Check out my other list Forbidden Love and Taboo Relationships.