@blue-san:
In my country, women claim they have that (6th sense)…
But they also claim men can only think about one thing at a time and I know thats not true because we always think about a certain thing no matter what we are doing...
In my country, people have a sixth sense that allows them to roll around in their own feaces and bark at the walls inside a loony bin.
YO RETARDIA! Get commited.
I apologize for ze vall ov tixt!
I would also like to add that I believe it's not that crazy a theory, or maybe something related to that.
The possibilities:
-BB had a conjoined malformed or weak siamese twin at birth who he absorbed through sheer force of will, for he would not allow himself to share a body or be weighed down by anybody, being too selfish and ambitious. In doing so he gained the vitality of two people, for he beat down and absorbed another soul or spirit of whatever. This would be another example of mind over matter like what Rouge did with Ace. Ridiculous, but plausible within One Piece's will can overcome all thematic. It could also be that he has a conjoined fetus on his back or some shit like that but it would be weird for me.
-BB has multiple personalities who are not fully aware of each other, and they each can house a different DF for they occupy and are handled by a different part of the psyche. It's a strange theory, I myself believe it would be too brainy for One Piece, and because DFs are tied to a more spiritual/demonic origin. It could be sustained though if BB was so fucked up in the head that his soul actually has a schism and can allow for two or more DFs. Essentially BB is the smart one in One Piece and he partitioned his hard-drive.
-BB is a D, and they can handle more than one DF because they're super awesome. Through sheer force of will, or through superior vitality or whatever, they can subdue the demons of two DFs so they do not tear the user inside out. I hope not. I mean this would open the door for Luffy and BB being special due to their heritage and simply too many Sasugay and Naruto references to handle. It could work though if BB has this inner strength but it's not attributed to Ds in any way. Besides, I think Luffy's lineage will give him another reason to fight further down the road, but should not be the source of his awesomeness at all. It would go against the One Piece theme.
-Truly evil people can subdue or get along with the devils inside the fruits. Of course this would enable so many pirates to eat 2 fruits that it would suck.
-BB is a cannibal or through some ritual or shamanistic belief can absorb the life force of others or strengthen and augment his own life force to be able to handle two fruits. He can still love cherry pie for dessert.
–------------------------------ REST AND COLLECT YOURSELF FOR ANNOYING THEORY ------------------------------------
There is a reason I believe that BB being able to have two powers is NOT due to his fruit. That he can steal a power from another body is due to his fruit, but that he can keep it without blowing up isn't. If it were due to his fruit, if his powers of darkness were ever inhibited by seastone, and the Yami Yami is keeping the demons in check, he would blow up. It's a huge weakness.
I know DFs aren't cancelled completely, but in the case of Logias(Ace, Crocodile) and Zoans (Marco) we haven't yet seen any power that has manifested passively when in contact with Seastone like Luffy's stretchiness has. Marco even stopped healing, so an inherent property of his DF which happens naturally without his control stopped working. This means that BB would probably lose his control over demons as well, even if it wasn't something that he had to control consciously. In order to circumvent this crippling weakness, where a seastone weapon (like Smoker's Jutte) would make him die it would have to be something else.
Of course it could be argued that Seastone weakens the demons inside, preventing them from killing the subject, making the point moot.
I know there's a bunch of things I'm assuming, and we still don't have a proper explanation, but from the current facts and Marco's comment we can be pretty certain that BB handling two fruits isn't due to his Yami Yami no mi but due to the strange makeup of his body. It would seem that wearing some eyeliner and concealant allows you to use 2 DFs. Sorry.
Marco's comment, if nothing else, makes it pretty clear it's something unique to BB and not his devil fruit, that's why I believe it has to be one of the options above, or something else we didn't think of.
Can anyone think of anything else?