I'm not entirely sure what about this 'One Piece' fanfic has made you furious. Maybe the author took some liberties with Akainu's character that you didn't like? For example, if they made him act out of character in a way that didn't seem true to the original 'One Piece' story.
It could be that the fanfic misrepresented Akainu's power levels. In 'One Piece', Akainu is a very powerful character, and if the fanfic made him seem weak or overpowered in an unrealistic way, that would be annoying.
I'm not sure specifically what that 'akainu this bites one piece fanfic' is about without reading it. It could potentially be a fan - created story in the One Piece universe that focuses on Akainu and some sort of 'biting' action, which might be a metaphorical or literal element in the story.
Considering Luffy's character development, he has always been against those who harm his friends and the innocent. Akainu has caused great harm, especially during the Marineford War. If Luffy continues to grow in strength, and if the story progresses in a way that pits them against each other again, there's a chance. But the Marines also have their own ways of protecting their top - ranked officers, so it's a complex situation.
If Akainu crossed over to a more peaceful part of the One Piece world, like the Fish - Man Island, his aggressive personality might be toned down a bit. He would be surrounded by a more harmonious society, and he might start to question his extreme views. However, his sense of justice (as he sees it) would still be there, but he could become more diplomatic in his approach.
Another aspect could be that the reader is a pirate who has a run - in with Akainu. Instead of the expected hostility, there is an instant attraction. The story could explore how they navigate their differences in values, with Akainu representing the Marines' strict code and the reader being a free - spirited pirate. As they interact more, their relationship deepens.
The fanfiction could start with Akainu being injured and the reader finding him. Despite knowing who he is, the reader decides to help him. This act of kindness plants the seed for their relationship as Akainu is not used to such selfless acts towards him.
You could try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). Just type in the title 'akainu this bites one piece fanfic' in their search bars and see if it shows up.
Well, Akainu could cross over into a fan - made version of the One Piece world where the Yonko are all united against the marines. He finds himself in the middle of this conflict and has to decide whether to side with the marines who he used to be a part of or join the Yonko for some self - interested reasons. He could also have a change of heart during this crossover and start to see the pirates' side of things, which would be a huge character development for him considering his strong stance as a marine in the original story.