One common plot device is the use of magical artifacts. For example, a magical amulet that has protective properties could be given to Harry. This amulet might be able to detect the presence of the stalker and create a shield around Harry when the stalker gets too close.
Another sign is over - monitoring. In many stalker friend stories, you can see that the stalker friend constantly checks your social media, texts you too often, and seems to always know what you are doing. For example, if you post a photo on Instagram and within seconds they comment with details about where you are or what you were thinking when you took the photo. It's a bit scary.
Perhaps it's a neighbor who has some sort of mental illness. They might have developed an obsession with the main character for no clear reason. They see the person through the window and start to stalk them, seeing them as an object of their strange fixation. Another possibility is that it's a criminal who has randomly chosen the house to target. They might be casing the place for a robbery, but their presence in the window makes them seem more like a stalker.
The motives could be many. It might be obsession. Maybe the stalker has developed an unhealthy fixation on the recipient, perhaps because of something they saw or heard about them. It could also be revenge. If the stalker feels wronged by the person in some way, they might use the mail to intimidate. Another possibility is mental illness. Some people with certain mental disorders might engage in stalking behavior without fully understanding the inappropriateness of their actions.
A character who could be the stalker is Gentle Criminal. He has that sort of flamboyant and devious nature that could lead him to stalk All Might out of some strange admiration or to prove himself as a worthy 'opponent'.
I don't think they are common. Schools are communities where people know each other, and there is a certain level of transparency. But it's important to note that any form of stalking, even if rare, is unacceptable. There could be cases where a student has some mental health issues that lead to this behavior, but it's not the norm in the school setting.
If you have a 'pregnant stalker', it's a good idea to keep a record of all her actions. Write down when and where she shows up, what she says or does. Then, you can take this information to the police. They are trained to handle such situations and can provide you with protection. Also, make sure your living and working areas are secure. Install security cameras if possible. And let your neighbors know about the situation so they can be vigilant.
No. Sometimes stalker stories can have a comical side. For example, someone might think they are being stalked but it turns out to be a misunderstanding like a lost dog that keeps following them around.
Yes. Stalker hero novels can be controversial because they may normalize or even glorify behavior that is not acceptable in society. However, some people argue that it's just a fictional trope and readers are able to distinguish between fiction and reality, but it still remains a point of debate.