The length of DB mangas differs. It depends on factors like the story's complexity and the author's vision. Some might run for just a few volumes, while others could have dozens.
The 'Chronicles of Narnia' is a great example of heros novels. The children in the story are heroes. They enter the magical world of Narnia and fight against the White Witch to save Narnia. Their adventures and the growth of their characters are really fascinating.
In my view, 'fiction db' is probably a term used in a particular field or industry related to fiction. It could be a database used by authors, publishers, or researchers to organize and access data about fictional works. But again, we'd need more details to know for sure.