WARNING: The following contains spoilers for One Piece Chapter #1020, "Robin vs. Black Maria," by Eiichiro Oda, Stephen Paul, and Vanessa Satone, available in English via Manga Plus and Viz Media.
One Piece's Wano arc is in an interesting state of affairs right now, particularly with the ongoing Luffy vs Kaido battle. Across this arc, the two have fought twice already and both times, Luffy has lost the Yonko called The Strongest Creature. Even in Chapter 1020, though he can hardly move, he still plans on kicking Kaido's rear. However, this is what makes Wano exhilarating and can prove to be a more thrilling climax in the end.
In typical shonen fashion, when the protagonist reaches the final battle against the arc's main villain, they stumble at first, receive some type of power-up, and manage to turn the tide at the end. Of course, not every shonen is so cut-and-dry and plenty find ways to subvert the audience's expectations. In previous One Piece arcs, Luffy loses his first bout with the main antagonist but manages to win the second; such examples include Crocodile and Rob Lucci.
In their first fight at the start of the Wano arc, Luffy used his Gear Four against Kaido, but the Yonko was able to knock the rubber man unconscious with a single attack. One Piece establishes how much stronger Kaido is than Luffy while also reinforcing that the goal of taking him down feels insurmountable. Since then, Luffy has trained and enhanced his haki control in Udon Prison with Hyo, leading into the Onigashima Raid.
When Luffy got his rematch with Kaido, he wasn't alone as Zoro, Kidd, Law, and Killer were by his side as well. This made Kaido feel like an even more powerful foe, especially because we just saw him defeat the Nine Red Scabbards by himself a few chapters prior. Furthermore, outnumbering him and Big Mom didn't guarantee victory for the Supernovas, but we did see their attacks still chipping away at the two Yonko.
When the story reached Luffy facing Kaido alone for the second time, it seemed like the fight could go either way. Luffy was able to infuse Conqueror's Haki into his attacks like Kaido, causing substantial damage. However, Luffy again lost in the end since he hadn't reached the same level of proficiency with it as Kaido. Unlike Goku reaching Super Saiyan or Ichigo unlocking Bankai, Luffy's advanced Conqueror's Haki was not an instant upgrade. He still needed to master the technique for it to help defeat Kaido, which makes the One Piece rubber man's struggle feel more earned.
Now in Chapter #1020, Kaido is facing Yamato while Luffy is recovering, but the latter hasn't given up on defeating the Yonko quite yet. There are two good reasons why Kaido is facing multiple opponents.
For one, it sells readers on this being more than just Luffy and Kaido's battle. The people of Wano have suffered for decades by Kaido's hand, and the Scabbards are fueled by revenge after the Yonko killed their master, Oden. They have both personal and utilitarian reasons in fighting Kaido which gives weight to seeing them fight as well -- even if it's a losing battle -- instead of simply putting all their hopes in Luffy.
The second reason is that the Wano arc is packed to the brim with characters. Some have even been introduced in Onigashima, like Yamato or the Tobi-Roppo. If this was simply about getting Luffy to Kaido, the story would be a lot more predictable. Instead, One Piece has what feels like a tabletop game with all these moving characters acting of their own accord. Kaido losing would be good for all of Wano, but Yamato has personal reasons in facing his father as well, which gives their current fight more emotional weight. You can't replicate that by having every character believe Luffy will simply save the day -- everyone has to contribute something.
Luffy will most likely face Kaido in the very end, and knowing Eiichiro Oda, the hype surrounding it will be cataclysmic. For now, though, we'll just have to keep cheering on Yamato while Luffy is recovering.
