Hey, guys. Long time no see. Something I'd like to share during my reread of Wano.
Now, we know Zoro vowed to avenge Yasu. At face value, it's pretty rare for Zoro to fight for a reason beyond just the duty of battle, but it runs deeper.
Among Yasuie's final thoughts, he asks of the Alliance to avenge him at the coming battle. I don't have the raws for this particular scene, but I imagine the intent was the same.
Zoro, as far as I can remember, is the only Alliance member to respond to this plea.
I think it's pretty significant that Zoro speaks on behalf of his allies, not just because of his relationship with Yasu, but the paragon nature of his time on Wano. That he is the one to respond to Yasu's cry for justice.
Further addressing Zoro's role as apparent savior, Shusui's and Ryuma's abduction coincided with when misfortune befell Wano. Like Wano itself went on a long night until the dawn, the Alliance, landed on Wano. With Shusui on hand. Though without the body of Ryuma, it was in the possession a swordsman who embodies the legendary samurai and the ideals of Wano.