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.
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.
The 'DB Cooper' story is about a man who hijacked a plane in 1971. He demanded a ransom of $200,000 and four parachutes. After getting what he wanted, he jumped out of the plane over the Pacific Northwest and was never seen again. It remains one of the greatest unsolved mysteries in American history.