I believe two things will happen in Wano with regard to Zoro’s character:
- His backstory will be expanded
- He will go through some major, needed character development
And I believe these two things will be connected through Kuina.
1) We’ve already got a lot of hints that the stuff in Zoro’s backstory will be fleshed out more: the “sunacchi” yell that Zoro likely learned from Koushirou; old man Hyo explaining Ryuo just like Koushirou did; hints that Shimotsuki village and Wano’s Shimotsuki clan may be linked, like the crossed swords symbol; the SBS 92 revealing a connection between Wano and the East Blue.
It seems we’re getting a backstory that will expand on Zoro’s master and village and their connection to Wano, rather than on Zoro himself. And I believe this is the chance for Oda to turn Kuina’s (admittedly pretty lame) death by falling down the stairs into a relevant plot point.
What if Kuina didn’t really fall down the stairs, and that was just an excuse Zoro and the other children were told? What if it’s revealed that the real cause of her death is more sinister? What if she was killed and Zoro will find out in Wano?
2) That’s how I get to the second point: Zoro’s character development.
For Oda, character development often means having his characters go through physical and/or psychological suffering. He makes them fall and reach their lowest point so that they can rise up stronger. See Law and Sanji as recent examples.
Often, Oda uses a trigger, or multiple ones, to set off their development: with Law, it was the reveal of Doflamingo’s lies and betrayal and his subsequent defeat at Doffy’s hands, while failing to avenge Corazon; with Sanji, a trigger was learning about Pudding’s true nature and her plan to assassinate him and his family. I believe Oda will put Zoro through something similar in Wano, making him fall to his lowest – something that hasn’t happened to Zoro in a very long time – only to have him rise to his highest afterwards.
Since the timeskip, Zoro has never lost, and only occasionally struggled. While he still laughs and goofs around, he’s also become more serious and distanced (some people even say boring), sometimes verging on too cliché in his badassery. He also never shows any weaknesses and few emotions. Zoro rarely outwardly expresses his emotions, and it seems anger is the only emotion he’s comfortable showing. In Wano, he seems to have got invested in Yasu’s, the people of Ebisu’s and Hiyori’s suffering at the hands of Orochi. But I don’t think Zoro’s current anger at Orochi will be the real trigger for the development I expect from him in Wano. It’s not personal enough, and anger alone is not enough. I think Oda will go further in challenging him emotionally.
Zoro is someone who meditates while training; who avoids distractions and lives a life devoted to the way of the sword. When he fights, it’s never a matter of personal motives as much as it is testing his own strength and worth. However, he too will fight for revenge, letting himself be driven by emotions, if the enemy touches something that’s personal to him. That’s what happened with Chopper on Skypiea.
So, this trigger that will set off Zoro’s biggest character development yet must be very personal, and what’s the most personal thing Zoro has? Kuina.
I don’t think even Zoro’s crewmates know about Kuina. She’s like his secret core motivation. The few times in the series we’ve seen him lose his shit and behave irrationally – while he’s usually a stable guy – are when he met someone who reminded him of her.
Through his encounters with Tashigi, I think Oda wanted to show how Zoro still has unresolved grief and emotional scars when it comes to Kuina. Finding out the truth about Kuina’s death could be the only thing that will really affect Zoro emotionally, making something snap inside him and causing him to fight purely out of revenge and personal motives, perhaps unlocking powers never seen before.
3) But why would someone kill Kuina? This is the most speculative part of this theory, but it’s based on what we’ve learned about Wano so far. I think she might have been killed by those hunting down the remnants of the Shimotsuki clan.
In chapter 953, Kawamatsu used the phrase “残党狩り” zantou gari that means “to hunt down the surviving members of a defeated clan”, which was a thing in feudal Japan. We kinda already knew Orochi in his paranoia tried to eliminate all his enemies, but thanks to that line we now know this historical “practice” exists in Wano as well. 11 years ago, at the time of Kuina’s death, Wano had been under Orochi’s rule for 9 years. Shimotsuki Ushimaru was dead, Shimotsuki Yasuie was believed dead, O-Toko had not been born yet (though it’s unclear if she’s a Shimotsuki as well). At the time, it might have looked like there were no longer any Shimotsuki left to hunt down in Wano.
What if Orochi then decided to turn to the Shimotsuki who had moved to the East Blue some decades earlier, to eliminate every possible opposition? They established “Shimotsuki Village”, so they weren’t exactly hard to find. Kuina might have fallen victim to Orochi’s assassins, who saw her with Wado Ichimonji that night and from that recognized her as a Shimotsuki. (Remember the practice of giving children a sword at birth? I think that could be the reason Kuina owned a Meito at such a young age.)
*Theory by akazaya9