Maki is stolen haki

Maki is stolen haki

I believe maki is created by stealing the haki of a slain adversary. Imu stole Joyboy's haki, Garling stole Xebec's, and Blackbeard will steal Shanks's. The themes and narrative of the story point to all three of these characters being closer in nature to thieves and frauds, rather than kings and gods. For this reason, I think it would make sense if their power is stolen, not earned.

Imu's maki

As stated above, I believe Imu obtained his maki by killing Joyboy and stealing his haki. We know for sure that Joyboy is dead, and that he fought against Imu in the void century. Putting these two together, the natural conclusion would be that Imu dealt the final blow that killed Joyboy.

Imu's maki is incredibly powerful, able to go toe to toe with Loki--who should be well above pirate king level--working together with the yonko who defeated Kaido, Luffy. The only character who has displayed a similar level of strength is Joyboy, who could send 5 ~admiral level combatants, the gorosei, packing with a simple release of conqueror's haki.

Imu's maki and Joyboy's haki both seem to completely dwarf the entirety of one piece's powerscaling as we've known it up to this point. This is why I propose a simpler solution: what if, instead of two freak outliers, we have one: Joyboy.

Garling's maki

I believe Garling stole Rock's haki when he dealt him the final blow at God Valley.

Oda has consistently portrayed Garling as a leader/important figure amongst the Gorosei, despite them all being clearly stronger than the Garling we saw at God Valley. Oda has also stated in a SBS that "[Garling] is strong. There's a reason for his strength". These two things make me think that Garling has received a massive power boost since his poor showing at God Valley.

Blackbeard's maki

Another character that needs a massive power boost is Blackbeard. He was last seen struggling with Law despite ambushing him with half of his crew, which is poor performance for a yonko, let alone a future Luffy-opponent. Blackbeard has already stolen both of his devil fruits, so stealing haki seems like the next natural step.

I believe the best candidate for blackbeard's haki is Shanks. Shanks has incredibly strong haki, shown by his feat of scaring off an admiral from several miles away, and being compared to Joyboy by the only characters that have experienced both his and Joyboy's haki. Blackbeard obtaining this level of haki would clearly take him up several tiers, much closer to where he needs to be to compete with EOS Luffy.

There is narrative significance to Blackbeard stealing Shanks's haki as well. From chapter one, Luffy has always been motivated to surpass Shanks. However, it would not make sense for Luffy to seriously fight Shanks during the massive world war the final saga seems to have thrown us into. Having a detestable villain like blackbeard steal his power would make more sense instead.

How is this achieved?

I believe the stealing of haki and converting into maki is only possible through usage of Imu's akuma no mi. So far, Imu is the only character to have shown total control over maki. Sommer's and Killingham can only borrow the power temporarily. But what if the power they 'borrow' was actually just being held by Imu for the moment, and it was actually originally obtained by them killing opponents with strong haki in the first place. Basically, Imu is like a maki bank for all who make covenants with him. You can deposit and withdraw your maki, and maybe even take loans.

This also leads me into a completely different theory, which I won't touch on much in this post, but is a fairly common idea. That blackbeard will steal Imu's devil fruit. This would allow him to steal the haki of his opponents, and would even explain why he didn't do so earlier with Whitebeard, or Garp. He couldn't do it yet.