Why Zoro is killing Kaido

een countless theories as to why ZKK (Zoro Killing Kaido) will happen and I've noticed a lot of them rely on evidence from external sources such as the OP Magazines, WSJ cover, and the dragon and tiger trope.
Although this is perfectly good evidence for the most part, I think there is enough evidence in Wano alone to suggest that Zoro will play a significant role in killing Kaido alongside Luffy.

In Act I:
→ Zoro meets back with Luffy.
→ Zoro then gets lost.

Why is Zoro lost ?

Oda needed a way to:
a) create a personal and emotional reason for Zoro to be invested in the war and ...
b) he wanted to give Zoro a legitimate reason to use one of Oden's blades instead of Shusui.

In Act II:

→ He meets Yasu and the rest of Ebisu town.
→ Gets Shusui stolen.
→ Meets Hiyori.
→ Witnesses Yasu's death. (fulfills part a)
→ Gets told that Shusui is a national treasure and should use Enma instead which he agrees to. (fulfills part b)

→ We see the panel of "For 20 long years, no one has been able to take Kaido's head" with Zoro's head clearly included. (942)
→ Zoro goes after Orochi but fails to kill/defeat him.

- He wants to "avenge" Yasu.
- He cannot forgive Orochi.

Why does Oda want to replace Shusui with Enma ?

Oda needed a way to:
c) have Zoro inherit Oden's will
d) and to give Zoro an Excellent-Grade sword which isn't black, so that he makes it black himself.

Ch. 953:

Enters Kawamatsu. His flashback reveals that:
- "When a companion dies, you take his sword and continue onward!!!" The companion who died would be Oden and Zoro would be the one continuing onward.
- "The soul that resides in a katana makes a samurai strong, and enables him to destroy his enemies!!!". The soul would be Oden's and it helps Zoro be stronger.
- The battle between Wano and the Animal Kingdom Pirates is not over and the swords shall not sleep yet.
- "Coincidentally", Hiyori proposes to give Zoro Enma. "The only one to have ever wounded Kaido". (And I expect an explanation later on as to why Enma is stated to be the only one to have hurt Kaido when both Enma and Ame-no-Habakiri seem to be used)

Ch. 954:

- Zoro accepts to replace Shusui with Enma due to Hiyori.

Ch. 955:

- It was assumed that Hiyori had died
- Hitetsu reveals to have waited 20 years to "bequeath" (leave (a personal estate or one's body) to a person or other beneficiary by a will) Enma and Ame-no-Habakiri to both Momo and Hiyori which then is inherited by Zoro.
- Enma is revealed to "split the earth to the bottom of hell".
- Zoro now possesses Enma (fulfills part c)
- Enma is stated to exude its wielder's Ryuo (flowing haki, 流桜, Flowing Cherry Blossoms) on its own, which is coincidentally the same haki Luffy is learning to use to be able to hurt Kaido and also happens to be the same haki which the scabbards used to cut/pierce Kaido.
- Hitetsu brings up the prospect of Zoro forging the black blade and potentially raising the rank. (fulfills part d)
- The chapter ends with the editors note saying "Inherited will".

It is not a coincidence that right after the explanation of companions picking up the swords of fellow samurai in Kawamatsu's flashback, this exact principle happens with Zoro picking up/receiving Enma.
Now, it is obvious that Zoro picks up from where Oden left off by picking up his blade, but ...

Where exactly did Oden leave off ? And what exactly was his goal ?

In Act III:


Enter the Oden flashback.
→ Oden reiterates the point that Orochi is a cowardly fool but goes to stop him directly just like Zoro did in Act II and fails as well. (968)
→ After hearing that Orochi gave Hyogoro to Kaido, Oden decides to strike down Kaido instead, the root of all the problems. (969)
→ Oden reveals he was on his way to cut off Kaido's head.(970)
→ Right when Oden goes in for the last and presumably the final attack, he is shown Momonosuke and is defeated by Kaido. (970)
→ Oden is dead and it is now up to his companions (his future ones) to finish the job he started (972)

Oden's goal of cutting off Kaido's head will be completed by Zoro as it's now up to the new wielder of the blade to continue what Oden started.

→ Zoro explicitly states that if him and Luffy take damage early on, they won't last to fight Kaido. Which confirms the fact that Zoro wants be involved in the fight against Kaido. (980)
→ Kaido's presence is stated to be similar to Hell. (984)
This is an important fact since it corroborates with the fact that Enma is the sword that cuts the earth to the bottom of hell.

→ Shinobu states that Oden "knew that Vanquishing Orochi would change nothing!! Even 20 years ago, the true enemy was Kaido!!!" (986)
This establishes that even for Oden, even though Orochi is the one whom he hates, the true enemy is Kaido.
Similarly, for Zoro Orochi is the one to have killed Yasu, but yet Kaido remains the true enemy he plans on fighting.

Now, all these plot lines don't mean that Zoro will be fighting Kaido one-on-one, this remains a group effort. The biggest mystery so far is how Oda will be able to have Luffy deliver the biggest hit to Kaido (since he is the MC) and have Zoro kill Kaido without taking away from Luffy.

Why is an Orochi fight unlikely ? (Assuming Orochi isn't dead)

→ Orochi is a snake and not a dragon, as confirmed by his fruit reveal in 933.
→ Ame-no-Habakiri quite literally means "Snake slayer" and as such I expect it to be used in the slaying of Orochi rather than Enma.
→ Zoro doesn't possess Ame-no-Habakiri, Momo is the one who possesses it.

What about King or the calamities ?

From what I've read so far, Zoro hasn't been foreshadowed to fight a single calamity. This doesn't mean it's impossible he fights them, but it decreases the likelihood.
With Sanji seemingly being the one to fight King (988), I expect Zoro to fight a significantly weaker opponent than a calamity as a warm up to the Kaido fight. If Zoro is to clash with any of the calamities, I don't expect it to turn into a long 1 v 1 fight.
Zoro (and the other strong members of the alliance) should be conserving their strength for the Kaido fight and I expect them to be kept away from the plot with small things such as gifters and etc.
 
At the same time this is Oda we’re talking about, someone will die but I can’t even predict who or how, great prediction though and I think this is a possibility
 
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