Monkey D. Luffy defeated Kaido using Haki and Gear 5, but clearly in the story, neither is his greatest strength. In fact, Luffy’s most powerful ability is his personality, which draws people to him and even turns enemies into allies. This was revealed by the creator Eiichiro Oda and will be showcased in a fascinating way during One Piece’s Final Saga.
Luffy’s Greatest Power: Turning Enemies Into Allies

During the Summit War, fans saw Luffy fight without the Straw Hat crew for the first time. Everyone thought he wouldn’t survive, but Luffy pulled off an incredible feat. When Kuma sent him to the island of women, he became the target of all the Kuja warriors, yet he not only survived but became the first man accepted on the island. There, Luffy turned enemies into friends, a pattern that continues throughout the story.
At the Marine prison Impel Down, all of Luffy’s enemies, including Crocodile, teamed up with him to escape. Then during the Summit War, Luffy fought with such resilience that Whitebeard was impressed and ordered his crew to protect him.
When Mihawk tested Luffy with his sword, Luffy was no match. Still, he survived thanks to his ability to make friends and have others fight alongside him. According to Mihawk, across all the seas, Luffy’s greatest power is his ability to gather people around him.
Gear 5 Is Powerful, But Only an Army Can Topple the World Government

There’s no denying Gear 5 is incredibly strong. In combat, it’s Luffy’s greatest asset alongside Haki. But overall, even Gear 5 can’t compare to Luffy’s talent for making friends.
Ultimately, the World Government can only be defeated through a united effort, which means Luffy can’t do it alone, no matter how strong his Gear 5 or Haki are. He needs a powerful pirate crew, but more importantly, he needs a strong allied army. Only then can he complete this mission.