Many One Piece fans wonder why Emperor Kaido, after defeating Luffy three times, doesn't kill the captain of the Straw Hat Pirates.
Some One Piece enthusiasts joke that Dark King Rayleigh is the theoretical mentor to Luffy, while the practical mentor to the Straw Hat captain is none other than Kaido himself. Throughout the Wano arc, Kaido has left Luffy alive after knocking him unconscious on three occasions. Being known for his brutality and preference for violence, why doesn't Kaido kill the Straw Hat captain?

Reflecting on their first encounter, when the rubber boy first set foot in Wano, witnessing the oppression of the people under Kaido's rule, Luffy lost his composure and immediately unleashed Gear Fourth in an attempt to defeat Kaido.
After a drunken stupor, even in his human form, Kaido easily overwhelmed Luffy. Instead of killing the Straw Hat captain, Kaido opted to incarcerate him in the Udon prison with the intention of subduing Luffy and making him a subordinate.

Despite his ferocious exterior, Kaido, through Luffy's actions and previously with Kid, seeks to recruit young pirates with sufficient strength to bolster the ranks of the Beast Pirates. At that point, Kaido doesn't view Luffy as his equal but rather sees the Straw Hat captain as a mere upstart.
This is once again evident in their second encounter. Despite recognizing Luffy's significant increase in strength since their initial clash, Kaido still lacks the determination to take the life of the Straw Hat captain. Luffy's mastery of advanced Armament Haki and his understanding of the power of Conqueror's Haki caught Kaido off guard.
However, instead of dispatching the Straw Hat captain, Kaido sends Luffy plummeting into the sea. Up to this point, Emperor Kaido still doesn't regard Luffy as a contender capable of challenging or impeding his power.

In their third confrontation, with proficient mastery of Conqueror's Haki combined with his combat skills, Luffy proves to be on par with the Beast Pirates' governor in a fair solo battle. Just as the Straw Hat captain is about to deliver a decisive blow to Kaido, a CP0 commander intervenes, causing Luffy to bear the full force of Kaido's devastating strike.
Once again, the Straw Hat captain finds himself unconscious as in the first encounter, yet Kaido still refrains from checking whether Luffy is dead or truly intends to take the protagonist's life. Instead, Kaido directs his fury towards CP0, enraged by their interference in his battle.
Kaido himself acknowledges Luffy's remarkable increase in strength despite being a relatively young pirate. He recognizes this strength and realizes that Luffy will be his rival on the path to becoming the Pirate King. However, similar to the previous two occasions, the Emperor has no intention of ending Luffy's life. Kaido's actions serve to assert his dominance over others.
Does this stem from Kaido truly valuing Luffy, or is he still under the delusion that the captain of the Straw Hat Pirates is not his equal?

With the final details of One Piece chapter 1043 revealing Zunesha, the giant elephant, hearing the drumbeats of freedom and the imminent appearance of Joy Boy, it's highly likely that person will be Luffy. When facing a completely new Luffy in the upcoming parts of One Piece, will Kaido regret why, despite having numerous opportunities, he never truly desired to take Luffy's life? What are your thoughts on this? Feel free to share your opinions!