Sakazuki, also known as Akainu, was introduced before the two-year timeskip of One Piece as one of the Three Admirals of the Navy and, thus, their strongest military asset at the time. Having been an Admiral, Akainu is one of the most powerful people in the world of One Piece. In the Enies Lobby arc, fans got their first glimpse of Akainu's terrible power when he blew up the ship carrying the people of Ohara. Shortly afterwards, Akainu was one of the stars of the Marineford arc where he challenged the likes of Whitebeard and his pirate crew, and made quite a name for himself.
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During the two-year timeskip, he rose to the position of Fleet Admiral of the Navy and, unlike any other Fleet Admiral before, he is openly challenging the supremacy of the Yonko in the New World. The debate of whether he is strong enough to compete with the strongest people in the One Piece world has always existed but does Akainu really have the power to stand next to the legends?
All the Admirals before the two-year time skip in One Piece had Logia Devil Fruits, with Akainu having the strongest of the lot at his disposal. While Aokiji was seen with the Hie Hie no Mi, which made him an ice human, Kizaru displayed the Pika Pika no Mi's light powers. Akainu, the strongest of the lot, demonstrated the incredible powers of the Magu Magu no Mi during the Marineford arc. With the powers of this Devil Fruit, Akainu can turn into magma at will, making him a magma man. Its destructive powers are in the same league as the likes of the Gura Gura no Mi of Whitebeard, one of the former Four Emperors of the Sea.
Furthermore, Eiichiro Oda has already confirmed that Akainu's Devil Fruit is one with incredibly high offensive power
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