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.
Well, 'db crossover fanfiction' usually involves taking characters or concepts from different 'db' related works and mashing them up. For example, if 'db' means Dragon Ball, it could be about Goku meeting characters from another Dragon Ball - like series in a whole new adventure that wasn't in the original. It allows fans to explore 'what - if' scenarios and expand on the existing lore in their own unique ways.