Kumadori said:"At the sea for a thousand years, and at the mountains for a thousand years, breathing the wind and drinking pure water, he passed the training of a Sennin. Enduring it all, he gained the Life Return. Humans are able to, from the hair on their head to their intestines, their toes, even to their most minute hairs, to concentrate their senses and stretch them to their limits, making it possible to control every part of their bodies."
I have two reasons for wanting luffy to have this
- He is made of rubber
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My favorite quote by luffy
His DF allowed him to do so much and get so much stronger and life return complements his DF. Giving yourself 100% control of a body that can bend and mold and stretch. Luffy could maybe even use it to be like a logia and just bend his body out of the way of attacks. Or turn his arms into blades or his hand into a battle axe or a shield.
Its really a injustice to his df to not learn to control 100% of his rubber body.
- The training part
From the way kumadori describes it seems like more of a spiritual/Mental thing than a physical thing (Bar and hold its Kumadori who is a nut job) but I think he wasn't lying. Out of the CP9 only him and Rob Lucci can use Life Return indicating that it's really not a brute strength skill. And He talks of a hermit he learned it from.
It would be nice to see luffy learn something spiritual or mental and not just something of brute strength from someone wise, giving him character development in wisdom and stuffs.