Chapter 3: Marine Based - 3
Which brought him to the final entry on the page.
Well, there was five originally, but he crossed off Fishman Karate. Since he highly doubted any fishman within their kingdom would happily teach him even if he did visit and the only thing that came to mind to learn it, was to head to East Blue, slaughter Arlong and his crew and force Kurobi to teach him the basics under threat of death.
Not something at all viable right now, even if Fishman Karate was one of the few abilities capable of harming Kaido due to the shockwaves one could produce with it and bypass physical toughness.
Alas, just not viable for him right now.
Which brought him to the most obvious on the list.
Devil Fruits
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Devil Fruits, the ultimate equalizer in this world. With some luck, a complete weakling could go from trash to being able to crush anyone without Armament Haki or sea stone weapons.
The problem being, getting his hands on one. If he wanted to buy one, they were ludicrously pricey. Even the weakest or ones with unknown effects, went for at least two hundred million beri.