Gender can be divided into two types "transition to another world" (Isekai ten'i) and "reincarnation in another world" (Isekai tensei). In almost every isekai story, the transported/reincarnated protagonist is a normal person in his original world. Usually, the protagonist is familiar with the parallel world, because it is a fictional universe pre-existing in his world.
Feel free to suggestions and/or questions. There may be details about the story in some of my summaries.
