NOTE: It's supposed to be merman but cut me some slack, yeah.
"Aren't you ever scared I'll pull you down and eat you?" Eren whispers against Rivaille's lips, when the sun is burning the color that belongs to royalty's jewelry, and the wind cuts him lightly with its sharpness. Rivaille only scoffs, leans back.
"Don't be stupid," Rivaille says, flicking Eren's nose, "as if I'd ever let you do that."
Eren laughs and wraps his arms around Rivaille's neck. The pirate straightens with a grunt, wraps his arms around Eren's bare waist.
"That tail is a lot heavier than it looks, brat," Rivaille drawls, and Eren only leans his head against Rivaille's.
"That's how I swim, you humans are too light for the sea to let you stay down long."
"Right," Rivaille says, doubful, and breathes against Eren's neck. "I wonder if they'll be a day when I won't smell seawater on you."
"Doubtful," Eren replies, and blinks, tapping Rivaille with excitement "What's that thing?"
Rivaille sets Eren down on the sand and turns to see what the mermaid was pointing to. He grimaces.
"It's a bird, looks like its wing is broken. Or it's stupid enough to think it'll find any bugs to eat out here."
"Bring it here," Eren demands and Rivaille shoots him an annoyed look but obeys, cradling the bird in one hand and dumping it on the sand near Eren. Its wing must be broken, if it wasn't flying away.
"Do birds eat fish?"
"Do I look like some bird expert? It eats shit, for all I care," Rivaille answers but Eren is already gone and returning with a small fish in hand, nervous grin lighting up his wet face. Eren sets the fish down and smiles when the fish pecks at the flesh harshly, hungry. After it's done, the mermaid leans down to stare at the bird.
"Sing a song for me, little bird," Eren says, but the bird only chirps.
"Birds only screech, Eren," Rivaille says, "besides, aren't mermaids supposed to be the ones singing?"
The bird hops away as Eren frowns. "I don't sing."
"Well, supposed to," Rivaille repeats, and Eren kisses him to shut him up.
The next time they meet Eren notices the sharp wounds on the pirate, and runs over each of them carefully.
"Your friend visited me the other day," Rivaille says as he drapes over the mermaid, letting the other examine each cut. Eren blinks, confused.
"Mikasa, I think it was," the man elaborates. Eren sighs, apologizing.
"She's always despised humans," Eren says, and Rivaille chuckles into his neck.
"You really are naïve," the pirate says, "she despises me because she likes you, idiot."
"Mikasa?" Eren frowns, "no, I grew up with her, I would know."
The pirate grabs Eren's face suddenly and crushes their lips together.
Rivaille breathes, "No, no you wouldn't."
"Mikasa," Eren starts and swallows when the other mermaid turns to look at him. "This sounds stupid, but, um, you don't like me, do you?"
Mikasa blinks slowly, before looking away. "I know about that human, Eren. All I ask is that you let me try."
"I never knew," Eren says lamely, because Mikasa has always been close and he thought that she hovers over him because she thinks he is a brat and young and naïve, but now it makes so much sense.
Mikasa laughs, and the sound cuts both of their hearts.
"No," she agrees, "no, you wouldn't."
Not all humans are like Rivaille. Eren forgets this when it matters. The net digs into his tail tightly and he hisses in pain as he struggles to get out but it's no use, the humans have caught him and they will not let him go.
When he breaks the surface he winces at the sun's burn and the greasiness of the pirate's smile when he sees Eren.
The pirate whistles as he reels in the net, "Look at what I caught here, captain! Now you won't have to see this filthy boat again, what with the load this pretty little thing will bring." The other crew mates crowd around the pirate, expressions of glee on their faces as they realize they wouldn't have to sail out to sea again.
"Stop it!" Eren shouts, "I can give you treasure if you want, as much as you need, just-" don't kill me.
"Ha! The thing's trying to bargain with us. Don't you worry your little head over it, your scales are more than enough."
No, Eren thinks as meaty hands grab the net, scrape against him as they pull him in and release the net, please, no, Rivaille-
"What are you little shits going on about now?" A familiar voice snaps, and the small gathering parts to let him through. Rivaille notices him immediately, falters in his step. It takes one second for comprehension to dawn, two seconds for fear, three seconds for indecision, something Eren never associated Rivaille with. Four seconds for the captain to reach for his swords, and then nothing, nothing at all.
Something slams against him harshly, a familiar weight, and there's commotion, shouts and screams.
"Shit, there's another one! Where the fuck did she get that sword-", cut off like something dying. Something bumps against him again, a groan, before a final push and Eren is back in the water, still cocooned in the net, but he's safe, the word churns itself in his mind as Eren catches his breath.
Something red follows him down. His eyes widen as warm hands reach for him, wrap around his frame through the rope, a weak breath near his ear.
(She was always better at jumping, wasn't she).
A sword rests where her heart should. She lies on top of him as her life bleeds out in front of him, staining the ocean a pretty red, and Eren stutters, reaches for her through the net.
"Mikasa," Eren pleads, "please, no, don't, don't, not like Mom, Mikasa, please."
She laughs weakly, closes her eyes and leans into Eren's hand, "I love you, Eren."
Eren cries, "I love you too, Mikasa. So please try, for me."
"Only as a fish may love a bird," Mikasa breathes. "With great pain and effort. I don't want to hurt you, Eren. You do not have to force yourself to love me because of of death."
"I don't- you're not forcing anything Mikasa, just-"
"Love me despite it," she says, and Eren chokes. The ocean stills, as if in mourning.
(He ends up having to use the blade to cut himself out of the net).
Eventually, he comes back to the shore, though every breath there feels like a betrayal, a stab. Rivaille is already waiting, clothes torn and face dirty with blood (it is the filthiest Eren has ever seen him, but he's sure more blood has seen those hands before).
"Eren," Rivaille breathes, relieved, and reaches for him, hesitates when Eren winces. He lets his hands drop.
"That girl," Rivaille swallows, "what happened to her?"
"She was infected by humans," Eren drones, and sighs when Rivaille looks away. He notices the wounds. "What happened?"
If Rivaille notes the slight reluctance he does not press. "Attempted mutiny. They knew they couldn't beat me."
It hurts that no one ever can. Eren smiles weakly. "I'm glad."
"Don't lie to me, brat," Rivaille snaps, and pulls him closer. "You aren't very good at it."
"No," Eren agrees, "I just thought you'd let it die."
Rivaille flinches back, and between them there grows a weed, a poison blooming, a distance.
(What he fails to notice is this: Mikasa did not die by human hands, she died by his. This is love).
Humans do not live as mermaids live.
"A bird may love a fish."
Eren runs his fingers over the slight crease of age in Rivaille's expression, the slight fold of death approaching in his heart, and closes his eyes as Rivaille grasps Eren's too soft fingers.
"But where would they live?"
Rivaille coughs and blood spills out, and Eren wipes it off quickly. Eren does not understand sickness as humans do, mermaids are not touched by it- the sea is that forgiving at least. He wishes he did, so he could lie beside Rivaille as equals, as something that could work. Rivaille falls asleep in his arms and the mermaid wipes the blood into the sand where it bleeds.
No, he thinks, as the sun dulls, the winds soften, and the ocean quiet. No, humans do not live as mermaids live.
But they bleed just the same.
He chokes in the water and he drowns in the air, he's not fit to be anywhere. So the little mermaid bows over the shore, tail a dull color in the water, skin burning lobster red, and he realizes what love is.
Love is watching someone die. Mikasa. Rivaille. Eren watches as the sun loses its zeal, and the sea stains dark with poison. He watches, and he waits for nothing at all, because the only mermaids granted immortality are the ones that don't want it.
The little bird sings,
Poor little mermaid, who's going to watch you die?