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 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'.
First, you need to create a compelling original character (OC). Think about their personality, backstory, and what makes them unique. Then, plan out the training regimen that the GARP will use. It could include things like martial arts training, survival skills, or leadership development. For example, if your OC is shy, the GARP could use group activities to help them build confidence during training.
In a fanfiction, Ace's own experiences and battles could be related to Luffy's metabolism. Maybe Ace has some knowledge about a special fruit or power that could enhance Luffy's metabolism. He could share this with Luffy, leading to a new adventure where Luffy tries to obtain this thing to boost his metabolism. Also, Ace's death could have an impact on Luffy's metabolism. Luffy could go into a state of shock or extreme grief that either slows down or speeds up his metabolism in an unexpected way.