Moments Explained
The Onigashima Raid is the most crucial part of One Piece's Wano Country arc and the Four Emperors Saga. It focuses on Oden's samurai, along with every other member of the Pirate-Ninja-Mink-Samurai alliance, attempting to raid Kaido's castle and take his and Orochi's head and free Wano Country from their tyrannical rule.
Luffy is shown to be quite strong and powerful right at the beginning of the series. However, in order to become Pirate King and find One Piece, it's not just about being powerful, it's about having a good, reliable crew. And Luffy knows this, right from the beginning. Which is why the very first thing he does is to look for good members for his crew. He knows the importance of having other people with him.
Zoro tries to fight for Luffy since he lies helplessly on the ground. Through Zoro's efforts, Kuma offers a deal to him. He tells him that he can take all of Luffy's pain away, but has to implant it in Zoro. Zoro agrees to this deal when Kuma says he could die from all of this pain. Kuma takes all of Luffy's pain away from him, gives a small portion to Zoro, then Zoro jumps into Luffy's pain (bubble).