An age-old question among the One Piece fandom is how Nami can hurt Luffy. Besides what should be a massive power difference, the Straw Hat captain’s body is made of rubber, so blunt force shouldn’t work on him. Despite this latter fact, Nami has consistently beaten Luffy to a bloody pulp whenever he annoyed her. Similar questions have been asked when Luffy’s other crewmates have similarly beat him up.
As far as anyone knows, there’s no in-story reason why Luffy can take these kinds of beatings from Nami. However, that hasn’t stopped people from asking questions and trying to figure out the answer. Many fans and even Eiichiro Oda himself have put forth their suggestions for how this phenomenon is possible.
What Possibilities Have Been Presented For Why Nami Can Hurt Luffy?
One Piece Nami beats up the crew
Technically, there’s already a canon answer to this question. According to Oda, what Nami is really attacking is Luffy’s spirit as well as his body. His logic was that since these beatings are often in admonishment with a strong sense of purpose; that facet of the beatings is what truly hurts Luffy and hits him in his spirit.
There may yet be something to this idea of beating up a Rubber Human with the right convictions. After all, Monkey D. Garp claimed he was able to beat his grandson with the familial love he felt for him. Perhaps hurting Luffy is a matter of the intent behind it.
However, this answer may be a result of when and how it was given. He gave this response as part of the SBS for Volume 43 when the Enies Lobby Arc was still underway. There may have been a concept that hadn’t yet been introduced to the story that Oda wasn’t ready to give, so he kept it hidden with a false answer. Even he admitted he wasn’t certain about the answer he gave here.
One such unintroduced concept during the Enies Lobby Arc was Haki. There were clues to this power system’s existence sprinkled here and there, but it would take years before it was formally introduced to the story. The introduction of Haki has led many fans to believe that Nami is using an underdeveloped form of Armament Haki to inflict harm upon her captain.
Another newly introduced possibility is the true nature of Luffy’s Gum-Gum Fruit, or, as it’s really called, the Human-Human Fruit Model: Nika. Besides giving Luffy the properties of rubber, this Mythical Zoan Fruit also allows him to invoke all sorts of ridiculous feats like bouncing off the air and reaching through eyeholes. It effectively makes him a cartoon character.
Could Cartoon Physics Have Something to Do With It?
Luffy Entering HIs Awakened Gear 5th Against Kaido
These applications of cartoon physics could be part of why Nami and a few others can beat up Luffy. It’s important to remember that these beatings are presented with a comical effect. Since Luffy’s powers are comical by nature, he may feel as much pain as it is funny.
Getting hurt only when it’s funny could also explain why Luffy’s enemies have trouble bringing him down. Since they fight Luffy seriously, they have to use old-fashioned Haki to cause lasting damage; that, or slashing and stabbing attacks. If Nami and Luffy ever got in a serious fight for whatever reason, it probably wouldn’t turn out nearly as well for the Cat Burglar.
Of course, it’s always possible that attributing these cartoonish beatings to any established story elements is overthinking things. Again, they’re done for a comical effect. The lack of logic behind them is never brought up and the damage done is quickly healed anyway; they have no profound effect on the story. They’re simply one of many running gags in One Piece and it seems like that’s all they’re meant to be.