Character development is key. Fanfictions explore how Ace and Luffy grow under Garp's influence. Maybe Luffy becomes more disciplined in some stories, or Ace learns to be more open - hearted, all thanks to their interactions with Garp and each other.
One possible plot could be that Luffy gets into a really tough situation during his adventures, perhaps surrounded by powerful enemies on an unknown island. In desperation, he calls out to Garp for help. Garp, despite his tough exterior, races to his grandson's aid. Along the way, he might reminisce about Luffy's growth and how far he has come.
In addition to Luffy and Garp, other characters could also play important roles. For example, some of Luffy's crewmates like Zoro or Nami might be present when Luffy calls Garp. They could add their own perspectives and reactions. Also, there could be some marines around Garp when he receives the call, and their reactions to Garp's decision to go to Luffy could also be part of the story.
One popular ace luffy garp fanfiction is 'The Bonds of Family'. It delves deep into the complex relationships between Ace, Luffy, and Garp. It shows how their different personalities interact and how their family bond influences their actions.
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.