There is a theory that everything we can imagine derives from something. Any creature or person that we come up with (for games, movies, books, etc) comes from something that exists or did exist. That's not to say a Daikiba existed exactly as we imagine it, but the idea could have formed from multiple creatures that have existed at some point (and the creature we see in game has traits from those various lifeforms).
The theory comes from the idea that if you were to be born in a dark room with zero sensory input and live there during your whole life, you would never be able to imagine anything. Your brain requires input (whether visual, auditory, etc) in order to form ideas.
If you look at any mob in EU, you can separate it down into lifeforms that, at some point, existed
