HolyJoker
The strongest technique in one piece is actually semei kikan because of the ability to manipulate you body You can use fat to nourish muscle and bone making them infinitely stronger as long as you eat(strength and defense out). for speed increase neurons, even for regeneration too. If you wanna be smarter and learn techniques faster manipulate brain, i know nothing about the brain SOOO the author can bullshit it. i think semei kikan is the way tto get rid of the 1 fruit per person and water weakness of devil fruit users.