I really like writing letters from Luffy's perspective, I can be a little more silly and childish, its a good change.
Anyway, this takes place before Enies Lobby, so around when they first arrive.
By the way, check out winkwankwonk's story, its like this one, only the letters are from Ace.
A letter to your (grand) parent
(By the way Luffy I didn't think you were stupid enough to spell "Dear" wrong so I didn't check it –Nami)
Dear Grandpa,
I haven't seen you in a while! But maybe that's a good thing considering I'm a pirate and you're a marine.
I know you're pretty upset about me and Ace not becoming Marines like you wanted us to, but Ace said not to listen to an old fart of a grandpa (his words not mine). But I couldn't become a Marine because I promised Shanks I would become a great pirate, and surpass him someday! I don't understand why you hate Shanks so much, he's such a cool guy!
I saw Ace recently too! He's doing really well, but he mentioned going after some guy named Blackbeard (Never heard of him, he sounds like he has a black beard though!). Maybe you know who Blackbeard is? If you do, I'd like to know! He sounds like a pretty bad guy. Is Whitebeard the good guy since white is the opposite of black?
I wish I could say I was sorry about not becoming a Marine, but I'm really not. The Pirate King has the most freedom in the seas, and that's what I wanna be. I don't want to rule the seas, I want to be the most free.
Besides you're pretty mean to me anyway, and you still are. I have no regrets becoming a pirate. But please don't find me and hit me, not again… It was bad enough that you hit Ace and I so much when we were younger!
From your frightful grandson,
Luffy
P.S. I had my Navigator edit this, so she might add some really rude comments! I don't think she means to be mean though.
P.S.S. Luffy please don't say my name to someone in the Marines, I really don't want to be found and arrested…. -Nami