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Law's character is based on the Napoleonic Wars and the battles of Trafalgar and Waterloo. This connection tells us everything we need to know about Law's future and the Man Marked By Flames
Oda was very intentional in the way he named Law. The battle of Trafalgar and the battle of Waterloo are two of the most important battles in the Napoleonic wars. In fact, Law's character has much in common with Napoleon-- from his name being based on those two battles, to the fact that he is a military tactician who prioritizes
Chapter referenceChapter 1100Law with a strange reaction to the mention of the MMBF
naval battle. In the battle of Trafalgar, Napoleon's naval fleets were overwhelmed and he faced a brutal defeat, losing much of his naval force. Three years after the battle of Trafalgar and after spending some time in exile on the island of Elba, Napoleon returned and eventually led his forces in the Battle of Waterloo where he was defeated once and for all and sent into exile for the rest of his life.
Law's defeat to Blackbeard was similar to Napoleon's defeat at Trafalgar-- a battle where his naval fleet was overwhelmed by a more powerful force. Law and Bepo escaped, swimming off into the ocean where they will likely be spending their own time in exile.
There is also a slight implication on Wano that Law is aware who the Man Marked by Flames is when he had an odd panel that hid his eyes when the Man Marked by Flames was brought up. It is also implied that the first time we meet the Man Marked by Flames will be on the sea with his jet black ship and whirlpools. I believe Bepo will swim with Law until they come into contact with a whirlpool and a black ship and they will be brought aboard the Man Marked by Flames' ship. Law will spend his own bit of time in exile on the Man Marked by Flames' ship and attempt to get his revenge on Blackbeard.
Much like how the first fight against Blackbeard was similar to the battle of Trafalgar, the second fight will be similar to the battle of Waterloo. Law will be stronger and he may even have help from the Man Marked by Flames, but ultimately, Blackbeard will prove to be too strong and he will defeat Law and the Man Marked by Flames and take the last poneglyph.
Finally, this sets up Luffy's fight against Blackbeard to carry even more importance, as they will each be in possession of the last poneglyph that the other doesn't have. Luffy will have to defeat Blackbeard for the fourth poneglyph so he can finally go to Laugh Tale.