Okay, so, this is an idea I just had. It's my return to attempting a crossover I haven't tried to write for years. But I think some of you might find this a welcome return, while others may wonder whether I am suffering from concussion or on drugs.

The crossover in question is One Piece.

Now, I have to say that the series is one I have a LOT of mixed feelings about. The setting is weirder than a bad acid trip, as are many of the characters and powers, the main character has to be one of the stupidest shounen manga characters to ever live (and Monkey D Luffy is up against a LOT of competition in tha regard: I'm looking at you, Son Goku and Naruto!), and it took ages to get to the real meat and potatoes of the story. In fact, for a long time, I stopped reading about halfway through the East Blue Saga, which goes to show how quickly the series lost my interest.

But, to give it its due, it has some very creative fight scenes and superpowers, the comedy can be pretty good when it isn't just weird or puerile, and there's still some interesting characters on both sides of the divide. Plus, there's a surprising amount of worldbuilding, even if it took until much later in the series for it to be truly implemented, from what I've gathered. And while I haven't seen the live action series itself (streaming services can go die in a hole), the clips I have seen of that version of One Piece were great, and it was the news of the series coming out that inspired me to go back and finish the East Blue Saga.

But how to do a Potterverse crossover? Longtime readers of the Cauldron may remember an initial attempt, which was a Harry/Nami story called Mare Nostrum, a title I eventually reused for a oneshot crossover with Blue Submarine No. 6, but the One Piece crossover never made it beyond the first chapter (which is in Chapter 75 of the Cauldron, in case anyone is interested). There's a reason for that: I thought Harry would, as I would, get frustrated with Luffy's mind-boggling stupidity pretty damn quick. Also, Harry, as a wizard (and a young one at that) would be both too OP and too weak for the One Piece world, being very much a glass cannon. Adult Harry would be another matter entirely, but there weren't many pairings I could make work, not without reading further into the series (as of writing this, I'm nearing the end of the Baroque Works Saga in the manga).

As for the pairings, well, there aren't many who interest me in the first couple of sagas. They pretty much amount to Nami, Princess Vivi, and Nico Robin. Nami and Vivi's younger ages presented problems, as Harry would have to be about Hogwarts age, and the problem of him returning to the Potterverse would inevitably turn up. On the other hand, a post-Hogwarts Harry would work nicely with Robin, IF he could get over the fact that she was an assassin working for a brutal mercenary organisation in order to destabilise an entire country.

Part of the problem was the One Piece world itself. Virtually every crossover takes place in it, and I didn't want to retread old ground. I considered bringing in one of the One Piece characters to the Potterverse, but wasn't sure how, and at the time, I was working on making it Nami.

But then, I realised Robin had potential. There's a number of gaps in her life between going on the run after the Ohara Buster Call and joining Baroque Works. Her father is unknown. What's more, there's plenty of parallels between her life and Harry's: she lost her parents early in life, she was raised by an uncle and an abusive aunt (though Harry's uncle was also abusive), they had an unwanted reputation foisted upon them...you get the picture.

This story came out of a number of what-ifs. What if Robin's father was from the Potterverse? And what if she somehow made it to the Potterverse at a young age? A world where she was, in theory, safer than she was in the One Piece world?

Admittedly, I haven't read the parts where Robin's past is examined, though I have read the wiki and watched a few clips on Youtube. Just think of any OOC moments as this Robin actually getting to relax a little for some months in the Potterverse.

As usual, there's no guarantee of this becoming a full fic. But honestly, I want it to in some form or another...

ÁNTHOS

CHAPTER 1:

AWAKENINGS

Wealth. Fame. Power. Gol D Roger, or rather, Gold Roger, the King of the Pirates, attained this and everything else that world had to offer. Fittingly, his last words before he died, executed by the forces of the World Government at Roguetown, sent countless souls to the sea.

"You want my treasure? You can have it. I left everything I gathered in one place, even the One Piece. Now, you just have to search the entire world for it..."

These words lured so many to the seas of the world, especially the perilous Grand Line. All in pursuit of dreams they never dared imagine. Some for wealth, some for glory, some for power, and others for the sheer adventure of it. Yet it has been agreed that Roger's words sparked off tinder that led to the firestorm known as the Great Pirate Era.

Yet few knew that Roger had sparked off this blaze partly because he had learned something of the truth of this world, a truth the World Government would go to great lengths to conceal. While he went to his death with a great smile, you couldn't say the same thing about the inhabitants of Ohara. A scant few years after Roger died, Ohara and its Tree of Knowledge was consumed by flames and explosions, its citizenry demonised as being insurgents who had to be stopped, no matter what the cost.

In truth, it was sheer genocide. The destruction of Ohara wasn't in the interest of saving lives, but keeping the status quo in place. It was a demonstration of the Buster Call, an atrocity used in times when overwhelming force was needed, and any culpability by the Marines or the World Government was buried under lies and denials.

And the sole survivor of Ohara? A child of eight years, a girl who never knew her father, and only knew her mother's embrace, at least since infancy, in said mother's dying moments. A girl who was allowed to leave by the whims of two of the Vice-Admirals of the Marines.

For five years, she was forced to go on the run, learning that the kindness of strangers could conceal treachery, that self-reliance was needed. Harsh lessons for any child to learn, but she was a good student. Her innocence and childhood had died with her island, with her people. Dubbed the 'Devil Child', and falsely accused of destroying Marine ships, all she had were her clothes, her wits, powers from a Devil Fruit, and a keepsake from her mother, one she was loath to part with even for the money she needed for food.

It wasn't just the Devil Fruit that gave her powers, though. She used power that was rarely seen on this world. It was a boon in helping her escape from the law or from ne'er-do-wells.

The trinket her mother gave her prior to her death was something her father gave her mother, that was all she knew. And yet, one day, it would save not only her life, but her heart and soul. Ambushed by brigands, she used the other power in desperation, infusing it into the trinket…only to end up somewhere else.

In fact, she ended up on another world.

For the first time in years, the so-called Devil Child received genuine love and affection. True, she learned of her father, and despised him for his crimes, and many people hated her for her father's crimes. And yet, she found a home with his relatives. The scars would never disappear completely, but after years spent on the run, to say nothing of the abuse she had from her aunt even before Ohara's destruction, she felt loved, safe, even welcomed. She began to heal.

She learned that, thanks to her father, she had magic. While her more logical parts of her mind sneered at such a thing, she also had lived on a world where Giants were public figures on both sides of the law, where an entire swathe of the ocean could not be navigated by normal compasses, and, let's not forget, superpowers could be gained by eating fruit that would also give you a massive weakness to being immersed in water. And she had eaten one of said fruit. Never mind all the other ridiculous things she had learned about on Ohara that she was told was true. Magic was a doddle by comparison.

Over several months, she soaked up her new relatives' teachings like a sponge, helped by her keen mind. She was already a lethal fighter with her Devil Fruit, despite her youth, due to her former status as a fugitive. But aside from spells and the like, she also learned about this new world, its politics, history, and culture.

After passing some tests, she was admitted to the Hogwarts School of Witchcraft and Wizardry. But before she could start at the third year level of schooling, she received unwelcome news. Firstly, her parentage was exposed to the media. But worse was to come.

Her father had escaped from prison.

And he was looking not only for her, but a figure of some notoriety in this world, amongst the mages, at least. A boy who miraculously survived when his parents didn't after being betrayed by her father to a notorious warlock. And she wondered, would she find acceptance here?

Time would tell…

This was starting to become a habit, and not a fun one either, Harry Potter thought as he roused himself from unconsciousness. He found himself once more in a bed in the Hospital Wing of Hogwarts, much to his irritation. And the school year proper had yet to begin.

Not that it had an auspicious beginning, what with that mess with Aunt Marge, then fleeing to Diagon Alley, and then learning an escaped killer was coming for him. And then, the cold in the train carriage, that thing opening the door…he remembered screaming, familiar screaming. And then, cold darkness.

Even as he sat up in the bed, he found a mug of something warm and familiar smelling gently pressed into his hands. "Hot chocolate," said a voice, an unfamiliar one for the most part. He looked up to see the careworn features of Professor Lupin, giving him a sad smile. "It's a remedy against Dementor exposure, Harry," he further explained.

Harry heard the harrumph of Madam Pomfrey, even as he sipped the hot chocolate, and most of the lingering pain and cold and hopelessness was chased away. "At least we have a Defence Against the Dark Arts teacher who knows his remedies this time. But why were there so many Dementors on the train?"

"Aside from the fact that they thought Sirius Black was on board?" Lupin asked with a scoff. "Someone probably told them that this poor girl was on board. Dementors may be monsters, but they're intelligent, even debatably sentient. They probably wanted revenge by proxy on Black for embarrassing him by giving the Kiss to his daughter."

Daughter? Sirius Black had a daughter? Harry looked to where Lupin and Pomfrey were gazing, to see a form slumped in a bed nearby.

It appeared to be a slender girl about his age, fourteen, with a short mop of glossy black hair framing her face. Those beautiful features, however, were twisted into a grimace of pain and fear as she moved in the bed, seemingly in the throes of a nightmare. Her skin, oddly enough, had a slightly tanned look to it, more noticeable compared to the more pale skin of a lot of British, or maybe she was of Indian extraction.

"What happened to her?" Harry asked.

"The Dementors happened, Harry," Lupin said solemnly, looking down at her. "Most people don't faint upon exposure, but…a few do, those who have the worst kind of memories. Dementors, by their very presence, dig up your worst memories, suck the warmth and happiness out of everything in their surroundings. Those are the prison guards of Azkaban. Anyway, don't you recognise her, Harry?"

"Should I?"

"She was in The Daily Prophet, in the issue about the Weasleys on holiday, I believe," Lupin said. "I recognised your friend from the photo."

"Ron sent me a clipping, but only of that article of them on holiday," Harry said. "I didn't see anything else from that issue."

"Whoever leaked her parentage to the Prophet ought to be punished," Pomfrey observed. "Apparently, the poor girl only learned of her parentage recently, and has been staying with one of Black's relatives ever since, the Tonks family. Holding the sins of the father against the child, I ask you. Anyway, Professor, I think she's waking up. Go get the other mug…"

It was a too-familiar nightmare. Running through the burning remains of Ohara, trying to get away from the fires, from the explosions. Tears streamed down her face.

As in her memories, she came across the hulking form of Kuzan, waiting for her at the shore. But unlike her memories, there was no boat, no delineated lane of ice to help her row to safety. No, Kuzan's expression was not sullen and solemn, but hard and cold, just like the Devil Fruit powers he wielded.

Then, arms grabbed her, arms belonging to the dead, halfway out of the ground. Her uncle and aunt, Clover, all the scholars and archaeologists she had learned from but couldn't save, Jaguar…and even her mother. All snarling, growling, or screaming at her, calling her the Devil Child, saying it was unfair that she lived when they had died.

They grabbed her, pulled at her, until her body was bent at unnatural angles. She knew what was coming next. She had inflicted the same sort of injuries to so many others with her own Devil Fruit. Oddly enough, she felt no pain, but the sudden vanishing of sensation below her waist was unnatural enough to make her scream.

And then, suddenly, she was enveloped in a block of ice, and she stared, unable to blink, unable to scream, as Kuzan stalked towards her. "True Justice is pitiless and cold," he said in his low, nasal voice. "You brought this upon yourself, Devil Child. You were born of criminals, and you will die like one."

With that, he reared back a fist, and smashed it into the ice block, shattering it, and with it, her body…

When her eyes opened, and she saw an unfamiliar face above her, a mug in his hands, she reacted more out of instinct than anything else. A pair of arms sprouted from the bed she was lying on, and grabbed his arms. Brown liquid sloshed out of the mug, dripping down, and to her surprise, she recognised the smell of hot chocolate.

The careworn man, after a moment of staring in shock, smiled, to her surprise. "Andromeda warned me about this. I'm Professor Lupin, your Defence Against the Dark Arts teacher for the year, young lady. The chocolate is for you. It acts as a treatment for Dementor exposure. Those damn things were swarming so close to you, according to Miss Lovegood."

After a moment, she remembered the eccentric blonde she had met on the Hogwarts Express. And she remembered the name Lupin, from what her guardians in this world had told her. "You're…my father's friend?" she asked.

At this, his expression soured. "Former friend, as I am sure you'd understand."

"I do. As far as I am concerned, he's just the sperm-donor," she retorted, deciding to remove the extra hands and arms, letting him hand the mug over to her. The hot chocolate was welcome, and she smiled. "Thank you, Professor, and sorry about that. Anyone else as badly-affected as me?"

Lupin indicated a bed next to her, and when she looked, she did a double-take. Messy black hair framing scrawny if somewhat attractive features, those emerald eyes behind glasses…oh, and of course, there was the infamous scar. A souvenir of the time a madman robbed him of his parents. She wished she had a scar to remind her of the time her home and loved ones were taken from her. A physical one, anyway. The scars she had suffered were on her heart, mind and soul.

Harry Potter. The Boy Who Lived. And the godson of her sperm-donor.

He wasn't staring at her like so many others, though. Oh, he was looking at her as if attracted to her, and she didn't mind that within reason. But there was no rancour or antipathy in his eyes.

Since coming to this world, it took her a long time to get used to not being viewed with hatred or cupidity. Of course, when her parentage was exposed in The Daily Prophet by that bitch Rita Skeeter, citing a 'respected source', that changed, but honestly, even then, it was nowhere near as bad as it was back on her homeworld. Not that it stopped things from hurting.

But he wasn't looking at her with any hatred in his eyes. Surprise, yes, wariness, well, she just sprouted arms out of nothing, even a little attraction. But no hatred.

After a moment, he said, "Umm, hi?"

She chuckled at his awkwardness, before sprouting a couple of extra arms on the bed, waving at him. "Hi. Sorry, I was having a nightmare, and woke up with Professor Lupin a little too close for my liking."

"…And the extra arms? What kind of magic is that?"

"A different kind to what you're used to. I might tell you about it later," she said. She wasn't sure if she wanted to, but if Harry Potter bothered to try and get to know her, she might tell him about the Bloom-Bloom Fruit. Still, she made an arm bloom from the side of his bed, and held it out in a handshake. "So, you want to introduce ourselves?"

After a moment, he smiled, taking the hand and shaking it with the hand that wasn't holding his own mug of hot chocolate. "Harry Potter. Though I'm sure you knew that already. And you are?"

"Nico Robin…sorry, Robin Nico," she said with a smile of her own. "My family name is Nico. It's good to meet you…"

CHAPTER 1 ANNOTATIONS:

So, Nico Robin's in the Potterverse as a teenager…but her father is Sirius Black? What the FUCK?!

Okay, so while the backstory will be elaborated on later on, the upshot is, prior to being Azkaban'd, everyone's favourite dogfather had worked as a bodyguard for Unspeakables researching the world of One Piece in Ohara. He and Nico Olvia had an affair, and because of that, he was dismissed, leaving him free to become the Potters' Secret Keeper, or so people thought. Of course, we know who the real Secret Keeper is. He did leave a special emergency Portkey that could bring Olvia to the Potterverse created by the Unspeakables…but Olvia gave it to Robin, and Robin didn't know how to use it until later during her time as a fugitive. There were only a few Unspeakables present on Ohara during the Buster Call, and those who were basically stole some books and notes on Devil Fruits and Poneglyphs, and fucked off without trying to save anyone. Croaker was far from amused when he found out.

There's no real way to tell who Robin's birth father is in One Piece canon. All that's said is that he died when Robin was young, and even that could be a cover story. So having Sirius have an affair with Olvia is plausible once you jump through a few hoops, and it gives an extra dimension of angst to Robin in this story, not that she needed more.

On the other hand, Robin has spent nearly a year in the Potterverse, being cared for by the Tonks family, who are her nearest family who aren't insane, imprisoned, or nasty pieces of work. For the first time in years, Robin knows what it is like to be (relatively) safe and loved. So while damaged goods and with a tendency to put walls between herself and others, she's in a much better headspace here.

She's not the femme fatale she appeared to be in her debut in the Baroque Works saga. True, she knows, thanks to years of being on the run and being forced to defend herself from belligerent Marines or pirates or run of the mill rapists, how to use her Devil Fruit to cripple or kill a person. So when she sees a strange man leaning over her bed just after she's had a horrible nightmare just after being exposed to a Dementor…well, that's why she attacks. However, she actually apologises afterwards, whereas canon Robin, at least prior to her character development, would laugh it off as her kidding.

Now, in other changes, I bumped the characters' ages up a year, so both Harry and Robin are 14 during Year 3. As for why Harry woke up in the Hospital Wing, thanks to someone tipping off the Dementors that Sirius' daughter was on the train, more Dementors attacked, worsening the effects.

And then, there's the change I made to Robin's Devil Fruit, specifically its name. I didn't want to be a weeb and use Hana Hana no Mi, and I honestly found the Flower-Flower Fruit name doesn't roll off the tongue as much, not to mention it seems misleading. Bloom-Bloom Fruit, however, feels more accurate, as new limbs bloom into existence. So don't go accusing me of acting like 4Kids, thank you very much.

No numbered annotations this time.