Which of the following details should go in the middle of the venn diagram?

The correct answers are:

1. Fantasy-based subjects
2. Teenage characters. 

The details that will go in the middle of the Venn diagram are details that both Harry Potter and the Twilight series share. These details are:

i) Both are fantasy-based- Both books are set in fantasy settings with fantasy subjects. While Harry Potter contains fantasy characters such as wizards, witches, goblins, talking ghosts, etc., the Twilight series contains fantasy characters such as vampires and werewolves.

ii) Both involve teenage characters- Harry Potter's main characters (Harry, Ron and Hermione) as well as minor characters (Draco, Luna, Neville and Ginny) are teenage witches and wizards. Similarly, the main characters in the Twilight series (Bella, Edward and Jacob) are teenagers.