I don't have enough context to determine exactly who 'garp' is. It could be a newly created character by the fanfic writer, or it might be a character from a relatively unknown story that is being incorporated into the 'ace fanfic'.
I'm not entirely sure specifically what 'garp save ace fanfiction' is about without more context. It could potentially be a fan - made story in which Garp tries to save Ace within the context of a particular fictional universe, perhaps related to One Piece.
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.
Well, without actually reading the 'ace whitebeards garp hits you fanfiction', it's hard to say for sure. But generally in One Piece fanfictions, it could be about battles, relationships, or character development. Maybe it shows Ace and Whitebeard facing off against Garp in an epic showdown, or perhaps it delves into their backstories and how they interact in a new, fictional situation.
One common theme is the clash of ideologies. Akainu has a very strict and uncompromising view of justice in his original story, while Naruto has a more forgiving and rehabilitative view. So when they interact in fanfiction, this clash often forms a central theme.