It should be like in "The Unscrupulous Prince Lai Pifei", the man is the father or brother (not his own) or the master of the woman, but they love each other.

Well, I have seen the explanation of this word before, and it is like this.

In ancient times, all living beings were fathers when they were teachers, so it was a false taboo to be with family members who were not themselves or their teachers.

The master is too provocative, but the apprentice is guilty. It is the case that an adopted daughter becomes a princess, and so is the one mentioned above.