ShadowWolf65

The Little Mermaid but with a few stylistic twists.

Gwi-ma is both the sea witch and the king of the sea. He has control over the sirens, which are mostly humans who made deals with him in the past. by the current timeline, the human world has forgotten about sirens and Gwi-ma, excluding the siren hunters (Rumi and co.) which happen to be the crown princess and her loyal handmaidens/guards/attendants this time around. the hunters and the sirens don't actually cross paths as much as in canon because sea travel isn't very popular for humans, and most of the ships that get ravaged by sirens are ones that won't be missed.

Jinu's chance meeting and rescue of Rumi happens very similar to the AU storyline. Abby is there too because narratively he has a little more emphasis than the other Saja boys and Jinu needs a best friend. + Derpy. Gwi-ma never finds out about this.

some time after Jinu gets away with rescuing a human, Gwi-ma decides to enact a plan that will destabilize the human kingdom he hates so much. he sends five of his strongest minions (saja boys) to the surface disguised as humans to basically start a coup against the crown. since his power isn't what it once was, the spell has some significant weaknesses: one being that it can't change them completely into humans. from sunset to sunrise they revert back to their siren forms (or if they become submerged in water, which adds some H20 style shenanigans for the fun of it), and also it requires the payment of something precious. RIP Jinu he's the only one of them left with something precious to offer, and that's his voice. He may or may not have a breakdown about this. The rest of the saja boys retain their siren songs while on land which gives them an edge when it comes to couping.

they reconnect with the main au storyline by washing up on the beach and getting found by Rumi (who turns out to be the crown princess. surprise!!) + her handmaidens. The boys are taken in as refugees. They fabricate a sob story about how they were musicians that were trafficked or something and get absorbed into the royal court because Jinu is such a good composer and the music is fire (even if the hunters can tell something is slightly off). Gwi-ma also included a clause in his spell that prevents the boys from revealing his plan to anyone, so it doesn't matter that the rest of them are still able to speak/write; they can't confess that they're sirens sent by Gwi-ma to commit murders. Jinu is sad about that because he's really falling in love with Rumi and doesn't want to hurt her or anyone else.

Also the spell lasts way longer than three days. Idk exactly how long but I'm thinking around a few months minimum. I imagine it takes some time to turn a very stable prosperous kingdom on its head.

Celine is the queen reagent because her sister the former queen died when her daughter was too young to take the throne. Celine has been on a quest to abdicate the crown to Rumi for years but Rumi is having too much fun slaying sirens out on the open ocean to take the burden of ruling. Rumi's half siren. if y'all seen the prince of egypt yk that once pool garden area where pharaoh's daughter finds moses I am in LOVE with the aesthetic of that place so we're highkey copy and pasting that idea into this palace specifically so Rumi has a private area where she can comfortably shift and sing without worrying about hurting anyone. Her ability to shift is contingent upon her conscious desire to change between forms (very unlike canon okay okay) so that's why she didn't shift after the shipwreck and Jinu had to save her.

The scene I rotate in my head is Rumi in full-siren form in her little prince of egypt garden which is in a completely secluded part of the palace. everyone in the royal court knows not to enter this part of the palace (except for Celine and Rumi) but when the saja boys are added to the court ig someone forgot to mention it. even zoey and mira give rumi her alone time while she's in there and they just assume she's meditating or something idk. ANYWAYS Jinu wanders close when he's exploring the palace and he hears Rumi singing and he's like "huh, that's siren song. i didn't know there were other sirens in the palace" and then partially because he's hypnotized by her voice and partially because he's curious he finds his way into the garden and sees Rumi and he's like whoooaaa that's a plot twist. Naturally Rumi freaks out. Jinu's about to turn around and leave because how tf is he supposed to process this but then Rumi's like "oh no he's gonna tell everyone" so she uses her siren song on him and tells him to stop. Now since Jinu is also a siren (albeit in disguise) the song technically has no effect on him. but like he's inclined to do what she tells him haha. Rumi doesn't know this. She's never really used her song on a person before and is so overwhelmed with shame that she has a breakdown RIP. Jinu can't say anything to comfort her because womp womp Gwi-ma stole his voice and also the spell prevents him from explaining to her that he's a siren and her song doesn't affect him BUT he feels bad that he's freaking her out so he just kind of tries to show her that he doesn't think she's a monster (aww) and we get a very romantic hand kiss (hooray!) Rumi will probably feel very betrayed when she finds out Jinu was a siren all along. idrk how the story resolves but ideally we impale Gwi-man like Ursula and everyone lives happily ever after.

Rumi's siren colors change after they defeat Gwi-ma in a parallel to her patterns in the movie but think like. betta fish. yk how they're super pale in those atrocious cups in the store but then as soon as you put them in a proper fish tank with live plants and clean water and plenty of space for swimming and jumping they explode with color. That's like Rumi. So I imagine her colors start out very pastel and faded and then the saturation gets cranked up when she finally accepts herself and reconciles with her friends and family.