Law and Kidd have now separated from the 5v2 originally to now a straight 2v1 against Big Mom.
I would call this fight the true start of the battle even in Chapter 1001 Its titled "Battle Of Monsters On Onigashima"
As well with Kaidou and everyone's clear intentions that this battle itself no matter which side wins will be that much closer to being the king of the pirates
And that leads us to the current Battle with just Kidd and Law Vs Big Mom
Now to the Explanation Law and Kidd have always been set to be involved in the defeat of Kaidou and Big Mom just for the simple fact that they're apart of the Worst Generation.... Not only will the be supernovas of the best generation to ever exist within the series they're also apart of the 5 Nova's who will lead this generation... Everyone fails to understand that them being of that generation is already a huge reason why them fighting Big Mom right now makes complete sense Doffy already explained to us age are meant to fight each other for supremacy of the New World.
If you remember the new world didn't use to have this much competition their were several pirates there beforehand yeah but it was clear during chapter 432 that the Emperors ruled over the New World. But because of the 2 years lots of changed the worst generation as entered and started making noise within it the marines have moved there base within the New World so that they'll appose these pirates more than before not to mention there forces have even gotten stronger since akainu has been fleet admiral.
Now this is important to note because whenever we got to the punk hazard arc the one to push forward this age that was steady for the past 2 years was one of the generation leaders Trafalgar Law. The character that our main protagonist made alliance with to deal with an emperor.
Oda has always been building for this war since Punk Hazard and has always thought of the Worst Generation being the biggest role in it (Wano has been the most supernova related arc besides Sabaody).
Now for the most important and blatant reasonings
Everyone is debating with each other of whether both emperors will fall or not but for the same reason oda has made it clear Kaidou will fall here he's done the same for Big Mom we're in the Vs Yonkou Saga since the ending of Act 2 we've gotten the narrator has said this Raid will affect a change for the entire world us being the readers didn't follow understand what this change would be until Cp0 has also said that The 2 emperors losing here would be a change for the entire world which is clearly true because 2/4 emperors falling disrupts the balance of the marines pirates and warlords (warlords being replaced with SSG)
Not to mention that Marco has repeatedly said that they'll be a change within age after this battle and has been pushing for the Worst Generation to be the ones to accomplish this task
Not to mention their is also the prophecy... I see a lot of confusion and also running around with this point but the prophecy doesn't just include that of Luffy and Zoro and Kaidou every person that was included on the rooftop will be part of the defeat in both Kaidou and Big mom if you remember Yamato was talking to Ace in the Flash back for Chapter 999 and how they're strong pirates making a name for themselves in the North South and West and the Strongest that'll come from The East fast forward 20 years later these Great Pirates have come to defeat Kaidou for the own reasons or even for Wano...Oden the man who understands and has read the true history says These pirates are the ones that'll defeat him. Big Mom is also included in this since she is in alliance with Kaidou she isn't making out as a yonkou leaving this arc they've even made it clear she'll be included in the defeat since Luffy said he wants to whoop Kaidou, Big Mom and Orochi all within this war multiple times.
One more thing I wanted to note is the group is the side of the protagonist are also suppose to show the antagonist side wrong... Apoo here says that a alliance of pirates will never be able to defeat emperors our sides is suppose to prove this point wrong.
