The story doesn't fully reveal who they are in a very straightforward way. They seem to be outsiders with their own motives and secrets. One might be a criminal on the run, another could be a wanderer, and the third has some sort of connection to the first two, but it's all left quite ambiguous.
One story could be about a wife who met a stranger on a train journey. The stranger was an old lady who shared her life story filled with travels and adventures. The wife was inspired by the old lady's tales and it made her think about her own life in a new way.
One scary story is about a hitchhiker. A girl picked up a stranger on a lonely road. The stranger was quiet at first but then started whispering strange things. She got so scared that she pulled over and let the stranger out. Later, she found out that there had been a series of murders in that area and the description of the suspect matched the stranger.
Strangers in scary stories can be menacing because they are unknown. We don't know their intentions, which creates fear. For example, in a story where a stranger follows someone at night, the person being followed doesn't know if the stranger wants to harm them, rob them or something else.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.