#text headcanons

a/n - sorry this is like so short 😢💔

The rest of the Undertale cast was born long after Monsterkind was trapped Underground. So, they don’t have first-hand experience of the surface (Gaster, arguably, does).

In the first 100 years, monsters traversed through the Underground and settled in the environments most adaptable to their bodies, finally establishing their kingdom’s capital in New Home.

Chara fell down approximately 300 years after the War. Of course, all the human veterans were long dead, and Monsterkind's existence was a mere afterthought to the Surface World. They knew, though, that Mt. Ebott was a dangerous place where nobody returns if one were to journey up there. Others were convinced that its dangers was just the stuff of old wive's tales.

Chara and Asriel found each other as children and died as teenagers.

Asgore declared his plan to take 7 human SOULs, destroy the barrier, and wage war against Humanity immediately after he found out his children were dead.

The CORE was developed by the Underground’s first Royal Scientist, Dr. Gaster, driven by the Underground's 'Enlightenment Movement': a surge of collective hope within the monster population to survive long enough for themselves and their progeny to see the surface soon.

It was only until Asgore took the third human SOUL that Toriel became sickened by her husband's plan and fled to the Ruins to try to prevent Asgore from retaining the four remaining SOULs.

Luffy's a mermaid who was raised in Fuusha village, just like in canon. And, just like in canon, despite being a mermaid, she SUCKS at swimming, a fact that Shanks finds absolutely hilarious. She still wants to become a pirate, she still eats her devil fruit and becomes a rubber mer(?), she still gets kidnapped by Higuma (who sees her as an excellent way to rake in cash, given how valuable mermaids are on the slave market), and Shanks still gives her his hat.

As a devil fruit user, Luffy's already atrocious swimming skills are now at zero. She can still breathe under water, but will sink like a stone, her strength sapped by the sea, and if she loses consciousness she'll stop breathing too. Needless to say, she stays out of the water, and the villagers come to accept that sometimes, mermaids just live on land.

Garp still comes back, and is still furious at her wanting to become a pirate (and inwardly, extremely concerned that a bandit tried to catch and sell her), and still takes her to live at Dadan's where she meets Ace.

Ace has no idea what to think of the weird fish-brat who he's now told is gonna be his sibling, and resolutely ignores Luffy. He's inwardly slightly impressed as Luffy continues to follow him through the mountain every day, not even particularly hindered by lack of legs and using a mixture of crawling, squirming, hand-walking, and ricocheting forward with rubber arms to move.

Luffy still meets Sabo the same way as canon, and is still caught by Porchemy, who at first is thrilled because a mer brat! That'll bring in WAY more money than the spare change Ace stole! But in the end, he loses his temper at Luffy's stubbornness and still beats her to a pulp.

Ace and Sabo still rescue Luffy, and they still exchange sake cups and become brothers.

Yes, brothers.

Because at this point, neither Ace nor Sabo nor any of the bandits, nor anyone really on Dawn island save Makino and Garp actually know that Luffy's a girl. Not even Luffy.

The three brothers promise to each other that they'll all leave the island when they turn seventeen, setting out to sea to become pirates (Ace and Sabo are honestly a little concerned, given how often people try to sell Luffy, and how despite aquatic appearances Luffy's vulnerable af in water, but decide to wait and see. They have seven years together, Luffy ten until seventeen, who knows how much stronger their baby brother will get in that time).

Sabo "dies."

Ace and Luffy continue to train, and things don't change until Ace is seventeen, shortly before he sets out to sea.

He's let Luffy crawl into his blanket to sleep with him (partially cold-blooded, Lu gets cold easily when inactive), and Ace realizes that his lil brother's chest feels a bit lumpy.

Concerned, he makes Luffy have it checked out by the bandits, who are shocked to find developing...breasts?

That can't be right...right?

Dadan makes a call to Garp, who snorts and says of COURSE Luffy's a girl, didn't he say granddaughter?

No, he had not, he had only mentioned "grand child."

Everyone is shocked, but none more so than Ace, who really doesn't know what to do with this new information.

(Luffy's not quite sure what a "girl" is, and when she asks Ace, Ace honestly doesn't know how to define "girl" either, so she doesn't get what the big deal is)

Ace realizes he's troubled because he can't remember the number of times he's rescued Luffy from potential traffickers, and the number of times he's heard the lament, "Pity it's not female, it'd be worth quadruple," from the kidnappers before he beats them to a pulp.

He already had doubts about letting Luffy go out to sea alone, three years after he's left. But now knowing that Luffy's a girl, and one of the most sought-after species that traffickers target...he knows the world out there is much bigger than a teeny peaceful East Blue island, and Luffy may not get lucky every time, and may not be strong enough in just three years.

But at the same time, it's not like he can order her to stay here. There's no way Luffy'd listen; the sea calls to her, freedom calls to her, and Ace understands that more than anyone.

Sabo, Ace thinks, what would you do?

The night before he leaves, Ace tells Luffy that there's been a change of plans.

He's still leaving for sea. He's going to get stronger, and work his way towards becoming Pirate King.

BUT, three years later, Luffy will NOT leave Dawn Island alone.

Ace promises that he'll come back, a stronger pirate capable of looking out for his baby brother (because girl or not, they exchanged vows of brotherhood, and that's something that can't be changed).

He refuses to let Luffy be his captain, he's still got his pride, but maybe, maybe if Luffy becomes strong enough, he'll let her be co-Captain.

Luffy is thrilled, because she wanted to be pirates WITH Ace, and grudgingly accepts the compromise, and promises to train and wait for Ace's return.

Ace leaves Dawn island, and makes a name for himself on the Grand Line (he's PISSED when he finds out he's eaten a devil fruit, because now how's he supposed to rescue Lu from drowning when he can't swim himself???).

He even eventually makes it to Whitebeard, and eventually comes to admire the man. Whitebeard invites him to his crew, and Ace honestly replies that a large part of him wants to accept...but he can't. He promised his baby brother that they'll be pirates and co-captains together, and he can't join another pirate crew without Luffy agreeing too. Even so, and he knows it's selfish of him, he wants to call Whitebeard his father.

Whitebeard tells him that Ace is already his son, regardless of where his allegiances lie, and gives him his blessing to return to East Blue to fetch Luffy. Whitebeard laughs that he can't wait to meet the lil brat that Ace speaks so highly of, and for Ace to hurry up and come back to the New World so they can meet.

Ace plans on traveling light, his former crew all choosing to join the Whitebeard pirates except for his first mate, Deuce. Ace loves his crew, but they're also his crew, and knows that he wants to make their crew with Luffy. So he thinks he and Deuce will be a good starting point (You're just bringing me along bc you want someone who can swim on the crew, Deuce accuses).

As they're planning on leaving, Marco lets slip to fellow commander Thatch that he heard that Ace's "little brother" is actually a super cute girl.

The next morning, Thatch shows up too, insisting that he come along, because hey! He's been with the Whitebeards for ages and hasn't been to Paradise in a while, he wants some change! And won't it be nice to have someone as reliable as him along, just until they get back to the New World and reunite with the Whitebeards? Really he has no ulterior motives like wanting to check out Ace's supposedly hyper hot baby brother-sister!

Ace is suspicious, but Thatch is already on board and the other Whitebeards are already waving so he lets it go.

(Shortly after they leave, Thatch discovers a devil fruit. Deuce tells him to sell the damn thing, it'll taste like shit, but Thatch thinks boy wouldn't it be great to be able to woo Ace's hot brother with a really cool devil fruit power. So he eats it, and yeah it tastes like shit, but now he can control Darkness which is sorta badass?)

(Somewhere on the Whitebeard ships, Blackbeard is still waiting for someone to find the darkness devil fruit, and well, it doesn't happen)

Before Ace returns to Dawn Island, part of him still hopes that Luffy looks passably like a guy. Having been to Fishman island, having befriended Jinbe, he knows that while mermen can still be targeted, mermaids are exponentially more vulnerable. He's learned the kinds of clothing that can help conceal tails, and is hoping that there's a slim chance they might be able to be pirates without the world knowing that Lu's a mermaid.

His hopes are shot when Luffy rockets into his arms at the dock, and his face is immediately buried in enormous tits that definitely weren't there three years ago.

Despite Ace's growing concerns (and red face; why does he feel so hot??? It's not his devil fruit...), Ace lets Luffy give Deuce a beating (why me?!) to claim her position as Ace's Co-Captain of the newly established ASL pirates (because if we're pirates together, Sabo has to be with us too!).

Luffy's gotten a lot stronger, but is still utterly ignorant of the outside world and the dangers it holds (such as the drooling Thatch who immediately wins Luffy over with his cooking despite Ace's burning glares). She's reckless and falls into the ocean every damn day, and while Deuce dives in after her and they've discovered her useful ability to talk to fish to ask for help, it still gives Ace heart attacks.

They still pick up more crew members while in East Blue, including Roronoa Zoro, Usopp, and Sanji, a pervy cook who competes daily with Thatch for Luffy's affections through food (Luffy appreciates the food).

At Arlong Park, Luffy encounters fishmen for the first time in her life. Arlong mocks Luffy's choice of friends and family, and invites her to join his crew made of her own kind. Fishmen and mer are the superior race, and Luffy will make a fine wife, Arlong says.

Luffy breaks his nose off, and Nami joins their crew.

Luffy's chosen mode of transportation is on the back of one of her sturdier crew mates, usually Ace, but often Zoro too. She unfortunately hates all the long skirts/robes Ace suggested for her to hide her tail, and so Ace has decided that being as intimidating as possible while carrying his brother glued to his back is the only way to go.

Needless to say, news of the former Spade Pirates Captain + Whitebeard Commander Thatch (are they an extension of the Whitebeards??) establishing the new ASL pirates spreads fast. That, and rumors that there's a beautiful young mermaid on board who can't swim. And despite the strength of the crew and their attempts at vigilance, Luffy's still dumb and gullible, and is kidnapped (and rescued) a dozen times before they're even on the Grand Line.

(after a few times, Luffy's uncharacteristically quiet, and privately asks Ace if they can break up the crew. She's holding Ace back; she not only made him come back to her, but half their adventures just seem to be her crew rescuing her. She's strong enough to defeat enemies, but not save herself. Ace tells her to shut up, and never bring this up again; they're BROTHERS, and he's not going to leave her behind or make her abandon her dreams when she can't accomplish them alone, and that's his choice. Luffy doesn't bring it up again, but works harder than ever to become stronger and earn recognition as co-Captain when the world seems intent on thinking of her as Ace's pet.)

During one of these kidnappings, Luffy's successfully brought all the way to an auction house before her crew can rescue her. An auction house that unbeknownst to them, was under investigation by the Revolutionary Army.

Liberating slaves is an unfortunately common mission for them, and Sabo's doing final sweeps as Koala frees the last of them when he notices a tank stowed away in a corner. He's familiar with these tanks, used to showcase mermaids in the rare occasions one can be caught, and it looks empty but he's still drawn to it for some reason.

It's only when he gets closer that he notices a mermaid crumpled at the bottom of the enclosure. She's completely slumped over, and he's afraid she's already gone, even as something about her screams with familiarity.

He's cracked the tank and has reached in to pull her out, when the wall behind him explodes in flames, revealing a furious Ace who snarls at the strange man with his hands on his baby brother...

...and then Sabo's memories come back.

~~

Something like that???? For an initial HCs dump????

This AU has continued! A LOT! Check out the comics, illustrations, and text stories for this AU under the Mermaid AU section of my One Piece Masterpost!

As always, REBLOGS, tags, asks, and comments greatly appreciated!

He smiles then, and it looks misleadingly gentle, and Koala can see why strangers may mistake him for a benevolent princely gentleman.   

But Koala knows Sabo. And all she sees is the manic sadism behind the oh so very fake expression.   

She cringes, because no, there is absolutely nothing romantic or exciting about this situation at all. All she feels is Doom.   

"Hmm?" she says, keeping her hands behind her back so he can't see them twist. In these situations, Koala's more than well aware that the more she talks, the more she incriminates herself.   

Many who observe their partnership are under the impression that Sabo's just the overpowered guy who beats people up and destroys shit, while Koala provides intel. And while it's true that Koala has intel, Sabo's the one who often personally extracts it from their most stubborn sources.   

In other words, what Sabo wants, he usually gets. It's usually a comforting thought, but not today.   

"Hmm?" Sabo parrots back, eyes lazily tracing over her face, and Koala frantically tries to keep her expression neutral as he searches for an opening. 

It's like when they were children, Koala thinks, when they played interrogation games with each other as assignments for Inazuma's class. Except this time, it's not Koala's grade on the line. And while Koala knows that her partner would never actually hurt her, he's also very capable of making life pretty miserable for her if she doesn't spill.   

And right now, she has a secret she'd really, really like to keep away from Sabo.

The secret being, y'know, the fact that someone proposed to his dearest baby brother.   

And even though it's extremely unlikely that Luffy understands the significance behind the gesture, she considers the gift hers, which, for all points and purposes...means she accepted.   

Koala does not want Sabo to find out about this, from her, at least right now, before she has more information.   

But, Koala glumly remembers, she's never actually managed to win any interrogation games against him.   

"You know," he says, voice deceptively light, and Koala wants to groan because here we go. "Luffy and Ace mean the world to me. They're not just my past, they make me who I am. Even when I didn't remember, they were with me, and I was with them. They're everything to me."   

Koala won't break. She tries to look for an opening without shifting her eyes, but Sabo's not an amateur and there are no escape routes.   

"It would truly be terrible, if something happened to one of them, something that should be stopped, that I could have prevented if only I had known."   

He's poking her defenses. He wants her to say, you're blowing this out of proportion, it's not that big a deal, or maybe you're overthinking this. Possibly even lie, I'm not hiding anything, or even counter, what makes you think I'm hiding something?   

Koala knows better. Those are all traps, all openings that he'd pounce on, and she's seen him rip people apart for falling for them. Koala won't give him the chance.   

He leans in close, and whispers in her ear, voice low and dark in a way that would make his fans cry, and his enemies cry too but for an entirely different reason. "You wouldn't know something that'd prevent me from fulfilling my duties as Luffy's older brother, now would you, Koala?"  

Well, Koala thinks snidely, depends on what you consider your brotherly duties, and whether they include homicide and starting a war with an Emperor.   

She says, "Mmm."   

Sabo, or rather his mouth, smiles. His eyes are a void. Koala's not used to be on the receiving end of this particular stare, and she isn't enjoying a moment of it.   

"Alright. If that's how you want to be. Let's figure this out together, now shall we?"   

Sabo's voice is calm, exaggeratedly patient, like a therapist. He never talks to Koala like this, but Koala still recognizes this particular tone, and cringes as she realizes which interrogation pattern he's chosen. It's one she's ill equipped to counter at the moment, and he no doubt knows it.   

Koala braces herself. Blank face, she tells herself, even breathing. He's using his stupid over-powered Observation Haki to keep track of your pulse.

"Well," he begins, "I know it's already about Luffy, because you're more nervous about me talking about her than Ace." It's stated as fact, and Koala blinks rapidly to moisten her eyes because she knows the real deal's starting now, and she'll have to avoid blinking when it might give her away.   

"And it must be something you found out during your Fishman Karate sessions, because you don't have any other time together, at least when I'm not watching."   

Koala isn't remotely surprised that he's monitoring everyone; after all, she's been doing the same. She wants to sigh but keeps it in.   

"It's probably something physical, because Lu can't keep secrets if she thinks of them as secrets, so it might have been something you saw...a scar, or a mark on her body? No? Then an object she has on her...Ah, there we go."  

Fuck you, I didn't give you any tells, Koala thinks indignantly, but she knows that expressing any annoyance will only confirm his guesses, and continues to refuse to speak.   

"You've been going to the kitchen more often than usual, but not during meal times, or even prep times, but rather lulls...times that you have no business in the kitchen, and times where only cooks are present, cleaning up or otherwise doing tasks that don't require their full attention...the perfect time to chat."  

Maybe I wanted a snack, Koala thinks, but keeps her mouth shut, because Sabo already knows when and how she snacks. This interrogation really isn't fair.   

"And as for the cooks in question...well, if it were Sanji, I'd just ask him myself, but you knew I wouldn't do that, right, Koala? You know I could get it out of him, so if it was him, he wouldn't know anything of value. But I don't think he's involved at all."   

Sabo looks at Koala expectantly. Koala stares right back at him, though her eyes feel very, very dry.   

"So the question now is, why would my dearest partner want to protect Thatch, Fourth Division Commander of the Whitebeard Pirates and temporary first cook of the ASL Pirates?" Sabo talks as though he's asking himself, but he isn't, and Koala's not fooled. She keeps her face blank. "I doubt it's a personal thing, after all, his intentions towards Luffy couldn't be more obvious, he announces it at least once a day. And given my partner's obvious little lesbian crush, it doesn't seem in her best interests to help him, no?"   

This does get a reaction from Koala, and her breath leaves her in a whoosh. Fine, make it personal. If he's figured out this much, it's only a few more steps till the answer, and at this point what does it matter. Koala glares, relishing freeing her face from its mask, and for a moment Sabo's back to his usual self, giving her a cheeky wink as though to say told you so. But then Interrogator!Sabo is back, because he's not quite done yet.  

Whatever. She tried, alright. It's not like she owes the Phoenix anything. She leans back against the wall, bringing her arms in front of her chest, and scowls, hoping her expression projects exactly what she thinks of Interrogator!Sabo at the moment. Sabo likewise drops his arms, because he knows she's no longer going to escape.   

"You're not protecting Thatch himself, because if you were we could solve it here, and it never needs to get out of hand. So you're protecting someone connected to him. The fact that you're being so stubborn, tells me that it's not just a personal thing, but something that could cause an incident, that would likely affect the Army. Which means, obviously, a Whitebeard pirate.   

"But I don't think it's just any Whitebeard pirate. They're someone high profile enough that it would be a big deal if I were to confront them, possibly jeopardizing any potential future alliances the Army forms with them, or drawing the eyes of the World Government. Which, they're already watching us, which makes me think it's gotta be someone even bigger than Thatch..."   

Which, of course doesn't leave much.   

"It could very well be old man Whitebeard himself," Sabo says, but he's shaking his head. "But something tells me it's not. And I know that some very interesting little blue birds have been stopping by the Merry, likely with letters for Thatch, but possibly also with unsolicited deliveries for my baby brother..."  

Your baby brother, chill with your possessiveness, does rubbing it in feel that good? Koala sniffs.   

"And as for why it's a big deal...you wouldn't be so secretive over a crush. Everyone on the crew has a crush. That can be dealt with. This is a few steps beyond, something you think would make me mad, right, Koala?”

Sabo pauses a moment, but it's for dramatic effect, because Sabo knows that Koala knows that he already has an answer.   

"So tell me, Koala. What did Marco the Phoenix give Luffy to try to claim her as his bride?"   

And well, there you have it.

"Bravo," Koala says dryly. "I see you're qualified for your position, Chief. I'll be sure to inform the Boss."   

Sabo tips his hat, and even though she allows herself to relax, Koala keeps her eyes trained on her partner.   

He's taking this calmer than she expected, to be honest. Interrogator!Sabo still hasn't fully faded from his face, but he's no longer giving off sadistic vibes, and has that little frown that tells Koala he's still sorting through his thoughts. His ability to remain composed is likely affected by the fact that they're still in Paradise, and the Whitebeard Pirates and the New World are still quite a ways away.   

Which is good, because it means Sabo can't just impulsively cause a massive incident on the spot. But it's also bad, because it means he's got more time to plot, and Sabo can come up with some pretty devastating things if given the opportunity.   

"Sabo, I barely know anything myself, and neither does Thatch," Koala says, finally willing to speak. "I'm working on getting more information. Don't plan anything rash yet. It could all be a misunderstanding."   

Sabo slowly nods, still quiet. Koala sighs.   

This might be a good time to bring up a certain topic, she realizes. She'd been thinking about it for a while now, but had wanted to give him more time.   

She first thought about it when the night after he regained his memories, she sees Sabo slip away from the Merry to pursue the ship that's transporting the slavers who tried to sell Luffy at the auction house. The slavers have already been passed in the hands of Army agents, all of the enslaved have been freed and are on their way to safety, and Luffy's back with her crew. Their job should have been over.   

Sabo comes back before dawn, accompanied by Ace who had likely transported him with Striker. He seems calmer than the night before, but Koala doesn't miss that his gloves are still damp from recently being washed.   

There've been other incidents too, in the short period they've traveled together. Koala's seen Sabo dangerously close to snapping (and actually snapping) more during the past few weeks than their entire decade together. And on one hand, it's understandable, but on the other...   

"You know," Koala begins, as gently as possible. "she's no longer the child you left behind. She's an adult. Even if this ends up being nothing, she may still find someone, one day. What are you going to do then?"   

If Luffy's in physical danger, protecting her is one thing. But what if it's something that she chooses?   

The change is subtle, but Koala notices when the last of the Chief of Staff fades from Sabo, as his head tilts downward ever so slightly. And all of a sudden he reminds Koala all too much of the tiny, battered child who stared at himself in the mirror when he thought everyone was asleep, touching his scars and asking, Who are you?

"I can't lose her, I can't lose either of them," Sabo says quietly, and he overlaps completely with the lost child, and ah, Koala thinks, because she gets it.   

That child, that self who was missing for so long, is back now, inside Sabo where he always belonged, where he always existed but couldn't be recognized. That child now takes up so much space, too much space, and still hasn't been fully reconciled with the adult that Sabo's grown up to be. Simpler, childish emotions and desires that feel too vibrant and raw, clashing with the adult's more weathered world view, aggravated further by all the darkness that Sabo's seen in their line of work.   

Sabo's less concerned about Ace, Koala knows, because even though Sabo loves both his brothers, Ace is like his other half. They don't protect each other, but function seamlessly as a single unit, a unit with one priority that stands above all else.   

Luffy.   

Luffy, who as a child, Sabo was able to protect from anything and everything in their isolated microcosm. Luffy, who as an adult, Sabo knows all too well is more vulnerable than ever, as proven by the very situation in which they reunited.  

A gilded glass tank, hidden away behind dusty curtains, with a dark, motionless shape crumpled at the bottom. Chains, chains, and chains upon bruised skin, and bubbles rising from parted lips, getting smaller and smaller as she slowly fades...

That was bad enough, but Koala doubts Ace or any of the others know exactly what the fate of a captured mermaid is, at least in the way that Koala and Sabo do.   

Koala understands, she really does.   

But she also knows the importance of freedom, not just to Sabo, but likely to Luffy and Ace as well.   

"Would it be losing her?" she asks, and child!Sabo flinches.   

"We vowed to be free," Sabo says, and he still sounds lost, like he doesn't know what the word means anymore. "And we will be." His hat shadows his eyes, and Koala can't imagine how they look at that moment. "But I don't want her to go where I can't follow."   

"Then follow," Koala says, because what else is there to say? "Follow, if that's your freedom. But you can't stop hers."   

"I know."   

She couldn't have known how Sabo would take her words.

~~

Part 8, we see more of Thatch.

Thank you so much for reading, and I hope you enjoyed!

As always, any comments are immensely appreciated and help motivate me to create more for this AU! ;A;

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