Once again is a One Piece time travel Fan Fiction written by TheVictor. A 7-year old Luffy is approached by his future self. It seems Luffy's entire crew died at the hands of Fleet Admiral Akainu right after defeating the Yonkou Kaidou. Luffy and his future self fuse together, making him both much stronger and much smarter as he repeats his adventure again, hoping to avoid the same fate as well as correct some mistakes.Easily the longest One PiecePeggy SueFan Fic in the entire fandom. It is the only one that has managed to reach Crocodile at all.
Almighty Janitor: How everyone see Luffy after he tells them about his brothers "Blue Gentleman Sabo" and "Fire Fist Ace", his friend Shanks, his grandfather "Hero of the Marine" Garp. Oh, and he gets to phone Whitebeard about the Blackbeard issue.
The funniest part is that the crew still doesn't know about Luffy's father.
Black Arm, Take Warning: Luffy will sometimes lose control of his Armament Haki when sufficiently angered by something. For example, Blackbeard's face.
Bunny-Ears Lawyer: Luffy kept his memories — meaning that until Robin joined, he was by far the most world-savvy member of the crew. And even with Robin he's still Mr. Exposition. He's still a manchild, though.
Crash into Hello: When Luffy accidentally uses Geppou for the first time, he ends up catapulting himself several dozens meters away...Right into Robin's bosom.
Curb-Stomp Battle: Many, many, of Luffy's fights, which make sense, seeing as he's a Yonko-level pirate in the middle of East Blue and, eventually, Paradise, the first half of the Grand Line. His fight with Crocodile was the only major fight he's had that wasn't one, but it was still a little one-sided. His fight with Mihawk doesn't count because it wasn't really a fight — they stopped as soon as Luffy saw that Zoro was okay.
Darker and Edgier: While still fun-filled, this fic deals with Luffy's knowledge of his crewmates', Sabo's and Ace's deaths, and how he will do whatever he can to protect them all. He often gets nightmares about everyone dying and you'd better not anger him when he's in a foul mood.
Deadpan Snarker: Surprisingly, Luffy, although pretty much everyone get it at some point.
The Dreaded: Thanks to his actions during the civil war and a subsequent interview, the entire world now knows that Luffy defeated Crocodile, resulting in this.
Flat "What.": How Luffy tends to react when the others (usually Sanji, Nami and Usopp) are stunned because he subverted Idiot Hero.
Groin Attack: In chapter 61, Luffy kicks Spandam so hard in the crotch that even Lucci winces in sympathy.
Idiot Hero: Aside from Robin and Zoro, everyone thinks Luffy is one. It's actually Subverted. He's childish and pretty much crazy, but he's quite smart and mature when he needs to be.
In fact, he even takes advantage of this to piss off his enemies — especially when he was stuck in that cage by Crocodile. By the time Vivi arrived, Crocodile was almost ready to tear his hair out because Luffy was annoying him so badly.
Kick the Son of a Bitch: Luffy does this both literally and figuratively to Spandam. It won't surprise anyone to learn that he greatly deserved it.
Manchild: Luffy, since he's technically an adult mentally — or at least as much as an adult that Luffy can be.
Only Sane Man: Robin seems to be the only one to understand Luffy is much smarter than he lets on, rather than an overpowered idiot with occasional bouts of common sense. That can be blamed on her general maturity and world-savviness. It also helps that while Luffy is physically seventeen, mentally he's around the same age as Robin, if not older, making it easier for Robin to connect with him.
Out of Character: Surprisingly averted. Despite Luffy being much more mature than in canon, he's still the Luffy we know — except he's technically over thirty years old now.
Official Couple: Luffy and Robin are set to become the main couple, but other than some bouts of Ship Tease, it really hasn't taken over the story.
The Stations of the Canon: Has this feel to it, though there are deviations — chances are that the story won't really deviate noticeably until around the Whitebeard War Saga.
Super Mode: For the most part averted. Oh sure, Luffy still has his gears, but he doesn't need to use them. He's only used Gear Third, but that was when he fought Crocodile. Justified that he's a Yonko-level pirate in the middle of Paradise — his baseline strength is probably equal to that of the upper tier Warlords.
Took a Level in Badass: Luffy again, of course (in the alternate future, he managed to kill Akainu. Too late to save anyone, but still!), but the other Straw Hats also got stronger thanks to his training. Sanji and Zoro can somewhat use Observation Haki.
Also, Future!Coby, who became an admiral and ate the Time Time Fruit. Luffy resolves to make sure he makes it to that level of strength again.
Luffy also gains higher bounties — his first bounty is 70 million and his second one is 160 million.
Took a Level in Jerkass: Justified with Luffy — after seeing his friends dying in front of him, he's determined to make them strong enough to survive this time around, as well as getting stronger himself. The recurring nightmares and subsequent lack of sleep doesn't help.
Troll: Luffy certainly acts this way towards all his opponents (especially evident with Arlong and Crocodile), but even outside of that, he appears to get a kick out of pissing people off (such as with the White Berets in Skypeia). His strength, general maturity, and knowledge of the future allows him to get away with this.