One common theme could be the exploration of their relationship dynamics. It might involve how they interact, whether it's in a friendly way or with some underlying tension.
I'm not sure about specific 'once ler x greed ler fanfic' off the top of my head. You could try searching on popular fanfic websites like Archive of Our Own. They usually have a wide variety of fanfictions in different categories.
Typically, in're monster fanfiction', there is a strong focus on the monsters. They can be depicted in various ways, either as fearsome or friendly. There's often a unique world - building aspect around the existence of these monsters.
Yes, indeed. The Re:Zero manga exists and presents the story in a graphical format. It might have some differences from the original source, but it still captures the essence and excitement of the series.
It's not ethical. Such fanfiction might contain adult themes like excessive violence, sexual content or other disturbing elements. We should focus on positive and family - friendly forms of literature.
I'm not sure exactly when it started. You might want to check on some dedicated literature forums or the author's official website for accurate information.