theTripleX_HSA
If not raikage than another perfect options would be Gol D Roger template well that guy is freaking pirate king that even without devil fruit can fight or even defeat whitebeard who is user of gura gura no mi + his monster strength and skill even by that Roger can defeat whitebeard and plus after he completed the Roger template than as reward u can have Roger sword 'Ace' to be given to MC for clearing Roger template as it will fun to see ace sword of Roger and plus all his similar power of his will be used against the marine will be quite amusing.