I'm going to explain what 4-sword and 5-sword style means here when Oda depicted 40 and 60 year old Zoro. Let's start with why I'm making this theory.
IS THIS JUST A JOKE?
At first I thought this was a joke of course but then I started looking at the comments written beside some other strawhats in their old age. In SBS 94, Ussop at 60 mentions missing a certain "her" implying either a dead loved one or someone he's not seen in a while. Then in the latest SBS 97, Chopper at 60 mentions having a drug that can cure anything implying he's created the Panacea of his dream.
Of course Oda makes the caveat of drawing a scenario where the Straw hats fail in these future situations to give himself plausible deniability that he's not just spoiling the story but the comments from Usopp and Chopper seem to signify that he's still considering actual stories when he writes these older versions. Usopp has some relation to a "her" and chopper actually made a cure-all drug. So given it seems Oda is putting actual thought into these, I'm going to assume he's doing the same for Zoro and so I'm going to explain what 4-sword and 5-sword style actually is.
(Yes this is a theory about Zoro after End of Series, but go along with me here for a bit)
THE RETURN OF ASHURA
I'm one of the very few who believe the 9-sword style Ashura will most likely never return but I'm going to play devil's advocate to myself since 9-sword style Ashura returning is what explains 4-sword and 5-sword style.
So basically we've already seen how 4-sword and 5-sword style would work, the same way Ashura works. They are "Illusions of Spirit with physical form".
ASHURA IS "ZORO'S FINAL FORM"
Ashura as presented in Ennies Lobby is basically the final form of Zoro. By this I mean there's nothing stronger than Ashura for Zoro and there will never be. Let's not forget, this is a WHOLE fighting style, 9-sword style. Meaning he can have both weaker and stronger techniques using the 9-sword style. Like the difference between Onigiri and 3000 worlds which are both 3-sword techniques but of varying strength.
The question is, why is Zoro's final form being presented to us not even half way into the story? I think the answer lies in comparing this to another Shounen manga, HunterxHunter. Spoilers ahead.
In HxH, the main character cuts his story short by summoning the power of his adult self as a sacrifice for his life. At the age of 12 he momentarily obtains all the power he would've had at his prime as an adult. This is basically what I think Ashura is, Zoro summons the final form of his own 3-sword style, which is the 9-sword style Ashura.
The difference between the two situations though is that Gon summons raw power he would have as an adult without actually gaining the experience he would've had as an adult. Hence even with the power, he's still using the techniques of his 12 year old self. While Zoro is the inverse, he's not summoning extra power as opposed to extra skill. The complete mastery of the 3-sword style is the evolution of the 3-sword style into the 9-sword style Ashura. But Zoro at Ennies Lobby and Sabaody has not mastered the 3-sword style so he cheats his way into summoning the 9-sword style Ashura as a final form instead of a power he evolved into.
To simplify, Gon summons his adult power with none of his adult skills while Zoro summons the final evolution of his style without training for said evolution and so the only power increase he gets is based on his current power at the time.
If Zoro were to summon Ashura in the present day, it would be stronger than Ashura in Ennies Lobby simply because Zoro himself is stronger but he'd still be cheating since he's not actually evolved into the 9-sword style.
4-SWORD AND 5-SWORD STYLE
Now what I believe 4-sword style for 40 year old Zoro is Zoro evolving into the 9-sword style. I use the term "evolving" to mean Zoro incorporates an extra sword into his "Base form".
"Base form" for Zoro here is like how we call Zoro using 1-sword, 2-sword, or 3-sword style Base form. He's fighting at his regular strength basically without a significant change in ability. 4-sword style is Zoro using a fourth sword as part of his Base form. And that fourth sword is an Ashura construct.
By this I mean Zoro still carries only 3 swords but now he can summon ONE extra arm or head with a copy of one his swords to use as part of his Base 4-sword style. And 5-sword style is again an extra either head or
arm with another sword.
In action imagine this, Zoro is trying to perform the 2-sword style Tower climb technique (the one used to dispatch Hawkins' Strawman), 4-sword style Zoro would only have to pull out one sword and then summon one extra arm and sword from his Ashura and swing just those two to perform Tower climb. And of course he can also create a bunch of techniques based on Four swords and which arm or head he summons from his Ashura.
The same then applies to 5-sword style then 6-sword style and then 7-sword style and 8 sword style until finally Zoro will be able summon the 9 sword style as his plain Base form ability and at that point, he's reached all he can ever learn about the 3-sword style.
END OF SERIES ZORO WILL NOT HAVE MASTERED THREE SWORD STYLE
The fact that Zoro at age 60 is still on 5-sword style then means that Zoro at the end of series will be nowhere near mastering his style.
This brings up the question, by Shounen rules, shouldn't a main character be at their prime or very close to said prime? I mean why are we following a main character now as opposed to later when they are actually in their prime.
This remains true for Zoro. Remember that Zoro already has the cheat to summon 9-sword style even now. And 9-sword style Ashura gets proportionally stronger based on current Zoro's strength. To compare with the 40 year old Zoro who knows the 4-sword style, the older Zoro who may be slightly weaker in physical strength will then have a weaker 9-sword style Ashura. BUT since 4 sword style is incorporated into 40 year old Zoro's Base form, his actual Base form could be stronger than Base form younger Zoro. Therefore we have a sort of balance, as Zoro's general physical strength goes down as he grows old, the 9-sword style Ashura gets weaker but since Zoro keeps incorporating more swords into his Base form, his Base form potentially gets stronger with time.
So if 21 year old Zoro is the strongest Zoro will ever be physically, that means that the Ashura Zoro summons at 21 years will be the strongest possible Ashura. Therefore Zoro at the end of series will be in fact the Strongest Zoro will be in Ashura as per Shounen rules. Just that his Base form will keep getting trained more and more until Ashura itself is just Base form for him as opposed to a form he transforms into for a limited time or other.
ZORO WILL NEVER MASTER HIS STYLE
If you've noticed 4 swords at 40 years and 5 swords at 60 years is seemingly very slow progression considering Zoro has 4 swords to go without that many years of good vitality to go. I mean he'd need another 80 years at the rate he's going.
It seems he'll never master the style even to his death and I think that's entirely okay. I mean it's Zoro. Of course it makes more sense that he'd train to the day he died. If he actually learned the entire style one day, then what? Would he just retire or something? Nah, it's better he trains to the end.
(And of course this leaves it open for the next generation to surpass him and actually master the style completely... *queue Buffy: Next generation with a 13 year old kid mastering the style*)
WHY HASN'T ZORO MADE PROGRESS TO THE 4-SWORD STYLE DURING THE SERIES?
There's a number of reasons for this. One is that he probably doesn't know he can. I mean we don't know if Zoro even knows what Ashura is exactly so maybe he's yet to even learn that he can do this. And it's possible he learns he can do this literally at the end of the series like as he fights Mihawk is when he momentarily pulls out only one extra arm and notices he can probably create a four sword style.
Second reason is a cope out but very possible and that's branding. Yes, Zoro is the 3 sword style user and Oda changing that to 4-sword or higher as the series goes on does affect the brand. Therefore Oda created the cheat code to have 9-sword style Ashura as a final form transformation instead of having Zoro progress to make 9-sword style his actual Base fighting style.
Third is that there's a whole other bunch of ways Zoro can get stronger in Base form. There's better swords, the haki training, the black blades and just muscle training. All these are enough to sustain a whole series of Shounen power progression and there's the cheat that all these automatically make 9-sword style Ashura stronger as well so that at the end of the series, even if Zoro has a ways to go with 4-sword style and higher, at least his 9-sword style will be at full power at series end.
SO WHAT EVEN IS ASHURA?
Who knows. Again, I never believed this will ever be explained or return in the story. This theory only exists because Ashura is the only thing that can explain how Zoro has 4-sword and 5-sword style exist outside of it being a joke yet other strawhats' older comments aren't jokes.
So if one day Ashura returns into the story or, even better, actually gets explained then I'll count this theory as even more confirmed.
Thanks for reading.
