We all know that Blackbeard got his hands on 2 devil fruits— Yami Yami no Mi and Gura Gura no Mi. The question being is that how did Blackbeard manage to get another devil fruit if he already has its own?
The Yami Yami no Mi is a Logia-type devil fruit that encompass the nature of Darkness. He can manipulate it at his will and can show devastating results. The power of the devil fruit shows that when another Devil fruit user touched its dark power, its devil fruit will be negated or temporarily shut off. Like the battle of Ace and Blackbeard, Blackbeard “stored” the power of Ace inside the darkness of the devil fruit temporarily shutting-off Ace’s Devil fruit power.
The main properties it has is that it can store Devil-fruit powers at his will. Blackbeard’s devil fruit is capable of capturing someone’s Devil fruit power, it depends solely on who’s he after. If the Devil fruit holder is still alive, it means the power is still inside him therefore Blackbeard can’t completely get it on his hands. But if the user died, the power has no beholder and therefore can be captured by the power of Yami Yami fruit, and store it inside the Darkness.
Think of the “Darkness” as a place where things can’t escape without light passing through. That is why Blackbeard was capable of getting the Gura Gura no mi.
I want to clear out that when a Devil Fruit user dies, the power stays intact. The power doesn’t leave the body of the holder instantaneously. It will leave the body once it can be reborn onto a similar fruit. We can say that the “darkness” created a way to store the power inside it by making a similar fruit made of darkness— basically its a storage room.
It’s just a theory, so it can be right or wrong. But I hope I was able to bring some interesting ideas to you guys. Let me know what you think!
Theory by Nul_lofi.