Chapter 816 of "One Piece" could treat fans to an epic encounter taking place between Luffy and the devious Big Mom.

At this point in the manga, the two characters are not yet lined up to take on one another, but it may just be a matter of time given how some of the events are playing out.

One reason to believe that a fight between the two will soon be taking place is the current situation that Big Mom has forced Sanji into.

Sanji is currently being forced to accept a marriage proposal from Big Mom that would essentially mean that he would no longer be a member of Luffy's crew, the Straw Hat Pirates.

Should Sanji decline the proposal, Big Mom has also threatened to gravely harm one of his friends, with Zeff being a likely candidate for that unfortunate honor.

Given Sanji's desire to keep his friends from harm, it is most likely that he will agree to the proposal, albeit reluctantly. This is where the Luffy–Big Mom encounter could take place.

Luffy has no desire to see Sanji be married off to someone he does not like, let alone actually lose him as a member of the crew.

Luffy will likely do what he can to save Sanji from his predicament, and that could very well include taking on Big Mom himself. Still, Luffy may already be thinking up ways to avoid as much trouble as possible. 

There are also speculations that Luffy may be working on a way to pit Big Mom against Kaido, in order to weaken both. Should Luffy succeed in pulling that off, he may be able to save Sanji, defeat Big Mom, and solve a lot of problems in the process.

Fans will likely be able to find out how Luffy eventually decides to deal with Big Mom in chapter 816 of "One Piece."