It might be common as it can be used as a plot device to show the depth of the woman's feelings for the man. If she desires this, it can imply that she is fully invested in the relationship and has no inhibitions when it comes to their sexual connection. This can add an element of passion and rawness to the story.
This could be about a mother teaching her son appropriate behavior in the context of storytelling. For example, she might be guiding him not to include inappropriate or vulgar content in the stories he tells.
Definitely not! This kind of theme is not suitable for fanfiction. Fanfiction should focus on creativity, positive emotions, and interesting storylines, not vulgar or inappropriate content.
In some fictional stories, it could be seen as a sign of extreme intimacy. It might represent a level of trust between the characters where the woman feels so connected to the man that she desires this act as a way to deepen their bond on a physical and emotional level.