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'.
Wilderness: Your disciple is courting death again. It's a novel about the primeval gods. The story told that the protagonist, Xiao Yi, had transmigrated to the Primordial World and became a first-generation human who was about to enter Jie School. He had activated the top-grade negative energy system, which could collect the negative emotions of others to strengthen himself. Therefore, he became the eldest disciple of Jie School who courted death all day long. His eldest senior brother often caused trouble, such as melting the swords of the sword tomb, refining weapons to blow up mountains, eating other people's mounts, and so on. Tongtian, the protagonist, was worried that his eldest disciple would cause trouble all day long. However, when Hongjun came out of seclusion and announced the God Deification Tribulation, Tongtian refused the God Deification of the Tribe of Severity and fought against the five Sages alone. The Tribe of Severity was facing a huge crisis. This novel was full of exciting plots, making people look forward to how the protagonist would deal with the Apotheosis Tribulation.
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.
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 popular garp fanfiction story could be about Garp's early days in the Marines, his training and the friendships he formed. Another might focus on his relationship with his family members in a different light, like how he interacted with his grandson Luffy during Luffy's childhood. There are also stories that might explore Garp's role in some of the major events in the One Piece world from a different perspective.