AN: Just a little something that popped into my head the other day. Obviously I don't own One Piece. Not set in any particular place or arc, although obviously we don't meet Dragon until Rogue Town and Garp in Water 7. No spoilers beyond the ones I just named. I've taken a bit of a guess with Luffy's mother, mostly by assuming that he must have had one, although no ones mentioned her.
5 Parents Luffy had and 1 he didn't;
1) His mother is his eternal parent, she was there in the beginning and he knows that she'll be beside him until the end. He knows she'd never leave him, so when he was ready, or rather when he knew he'd never be more ready, he left her. He left home and he left his mother behind, and despite that he knows they'll meet up again. They've chosen opposite career paths, for as long as he can remember she's hunted down bounties to put food on their table, and now he's a pirate with a million belli bounty. But he's always been honest about wanting to be a pirate, even when it made Garp mad, even when Makino and Dadan didn't think he could pull it off, she's always known and she never stood in his way. So he goes through life as he always has, running without a plan and jumping without looking and knowing with absolute certainty that it will all work out for the best, and that some day, some where down the line, he'll see her again.
2) Garp is not the best of parents, he's a marine through and through and he raises children like he leads men, with iron in his spine and a heavy fist. He's raised one son to be the leader of an army of anti-establishment anarchist and two grandsons to captain pirate ships. All three have million belli bounties on their heads and upon capture face execution. He's not the favorite parent either, he didn't give candy or presents, he gave lectures and survival exercises. In most worlds he would be considered an abject failure as a parent, and certainly his own son would agree with that, but for Ace and Luffy he's family. Frustrating and crazy as the old man may be, it's always been enough for them that he always comes back.
3) Dadan often rates as the lazy parent. She does what it take to make them survive, and draws the line at that. They know she cares, but she isn't there to coddle children, to wipe their tears or kiss a scrape better. She gets into the child rearing business because of blackmail. She provides the brothers with a home, meals, and occasionally a bit of her wisdom, learned from a long career of banditry. She shakes her head later to hear Garp complain about the poor life choices of his grandchildren. It was never a surprise to her to hear what path Luffy and Ace choose to walk, only that they actually flourished in their choices.
4) Makino is by far the best of Luffy's pseudo parents, though he doesn't always acknowledge it. She leaves him to his adventures and mischief, but her door is always open, with a glass of milk and a plate of meat, surrounded by helpful and healthy vegetables. She listens to his stories and laughs at his jokes, but she also scolds him and bandages his war wounds. Makino is the responsible one amongst all of Luffy's parents, she's also the only one who doesn't think responsible is a curse word.
5) Shanks is the fun parent. He's the one who stands farthest away from responsibility and closest to danger. He isn't always there, and there's really no way of knowing when he'll be back, but he cares in his heart and that always been enough for Luffy. Shanks is a dreamer and a pirate and if Luffy has to cross five oceans and take on every powerful man in the world, he will, for the right to follow the only father figure he's ever really had. Shanks is probably Luffy's favorite parent, the one who laughed with him, and at him, then jumped into the ocean and faced down a monster to save him.
1) He meets Dragon for the first time in Rogue Town, although he doesn't know it at the time. 17 years is a long time to wait and with everything else that's happened in his childhood he stopped asking questions about his father years before he met anyone who could really answer them. It doesn't faze him to hear that his father is the world's most wanted man, partially because he's gotten accustomed to a life of danger, but also because he can't really conceptualize that he has a father. His crew is amazed and the marines are shocked as Garp tells them about Dragon, but Luffy finds that he really doesn't care. With all of the parents that he did have, he never missed the one he didn't.