LawLu

LawLu is the slash ship between Monkey D. Luffy and Trafalgar D. Water Law from the One Piece fandom.

Canon
Despite Law's outward stoic demeanor and apathetic attitude towards Luffy, Law does seem to like him. He also seems to accept following Luffy's lead when it comes to carrying out their plans and tolerates the Straw Hat's captain taking the initiative in a lot of situations, even if it can annoy him from time to time.

The two first met at Sabaody Archipelago inside the Human Auction House, Law witnessed Luffy punch the Celestial Dragon, Charlos. He smiled at Luffy's defiance towards the World Noble and fought alongside him, as well as Eustass Kid, when the Marines surrounded the auction house. Following this, the two went their separate ways.

Law and his crew traveled to Marineford during the Summit War of Marineford to assist with Luffy's escape, and then later administered medical treatment to him. As he said, while Luffy would one day be his enemy, an enemy relationship is still a relationship and that it would be a "damn shame" for Luffy to die at Marineford. He then left Luffy in the company of Jinbe and Silvers Rayleigh before Luffy could thank him.

Following the time skip, Luffy met Law again on Punk Hazard after Law became one of the Seven Warlords of the Sea, he saved Luffy and Nami from the Yeti Cool Brothers. He then asked Luffy to form an alliance with him to take down the emperor, Kaidou. Luffy agreed, making their crews allies in a relationship (which Luffy perceives to be as practically a friendship, but Law sees as more of a professional agreement). Luffy often treats him very casually, like a good friend, something which Law usually frowns upon. Law has invested enough in this alliance that, despite it having nothing to do with their agreement, he decided to help Luffy and his crew save the kids on Punk Hazard, even though he himself only viewed them as a burden. He also has a lot of faith in Luffy, as he asserted to Doflamingo that Luffy would capture Caesar without a problem.

At the end of Punk Hazard arc, Law also objected to Luffy's decision to throw a party instead of leaving Punk Hazard, as he believed they were still vulnerable, though he still reluctantly joins them and has stew with Smoker. Though Law indicated that he wished to 'use' Luffy when forming the alliance due to the Straw Hats' great unpredictability and ambition, he instead feels like the one being used.

During the Dressrosa Arc, he stated that if Luffy were to die at the hands of Doflamingo he would be prepared to die along with him, as he felt a sense of guilt for dragging Luffy into a battle that was outside their original agreement.

Fanon
LawLu is one of the most popular ships within One Piece fandom, with more than 3000 fanfiction on AO3. Many fans like how their relationship has evolved over time, and how Law and Luffy have developed a sense of mutual respect, and despite having opposite personalities they generally get along; while Luffy is downright silly and stupid, Law is more stoic and serious in any situation.

A comic relief in fandom is how Law very often organizes a possible plan for some mission, and Luffy does not follow it ruining it, ending up being reprimanded by Law himself. On AO3, LawLu is the second most written ship in the One piece tag, and it is the most written ship for both characters.

Fandom
Law/Luffy Tag on AO3.

Trivia

 * Luffy is unable to correctly pronounce Law's surname, so instead, he calls him "Tora-o" (トラ男), which is a part of the "Tra" in "Trafalgar" and the Japanese kanji for "male". This is often localized as "Tra-guy" in some subtitled media, or as "Traffy".