Thank you AnimeTrashFTWBruh for this idea. Sorry if it's not what you had in mind.
~🐬~
"Quickly (y/n), swim!" your friend calls out, her voice coming out as a loud shriek.
A gasp escapes your lips as you push yourself to swim as fast as you could. You briefly glance behind you to see that a giant great white shark was right on your tail. A scream pushes itself from your chest as you feel the teeth of the shark dig into the flesh of your tail. You struggle against the strong jaws, desperately trying to escape. One of your arms flings and hit the shark on the nose, making it visibly flinch. You reel your arm back and repeatedly slam your fist into the nose of the shark. With that you manage to tug your now severely injured tail free. You remove your dagger from its place by your hip and stab the shark on the snout. You're relieved when the shark swims away, seemingly irritated. Just as you were about to head back home, you feel your eyelids getting heavy as you lose more and more blood. It isn't long before you fade into darkness.
~~~
The light haired boy walks along the beach, his bare feet kicking up the sand. The salty winds blow through his hair, dishevelling it. He lets out an irritated sigh as he tries to fix it, he ceases walking when he notices something lying in the shallows of the water. He takes a closer look, his brows furrowing at the sight. A young figure with (s/c) skin, (h/c) hair and a long (f/c) tail was lying in the water. He also almost instantly sees the bright crimson blood surrounding them. On their tail was a large bite mark, but luckily none of their tail had been ripped off.
He contemplates for only a moment before deciding to help the poor washed up... mermaid?
He leans down and picks her up with ease. He then turns back around and heads back home.
~~~
Your head felt heavy as you try to push yourself up on your elbows, only to slide back down onto your back. Your eyes flutter open and you look around to see that you weren't in the ocean. You begin to panic and try to get out of whatever contraption you had been put into. You could practically feet your heart beat out of your chest, your breathing began to speed up until your head felt light. You hear footsteps coming from somewhere else and panic even more.
'I don't want to become soup!' you scream in your head.
"Hey, calm down." a voice speaks in a rather soothing tone.
You snap to look over at whoever was speaking, to see a blond male with a blue and violet scarf tied around his neck. He had knelt down beside the container beside your head. Your eyes go wide and you stare at him, terrified.
"Please don't hurt me." You stutter, flinching away from him.
"No, it's okay," he attempts to soothe you, "I won't hurt you."
"How can I trust you?"
His eyes soften at your distressed expression.
"I saw you on the beach; you had a pretty nasty wound," he says, gesturing to your tail, which was wrapped up in bandages, "I brought you to my house and fixed your tail."
"Oh, uh," you mumble, "thank you."
"So, I'm Eridan." He introduces himself.
"I'm (y/n)."
~~~
It had been three weeks since you had been staying with Eridan. At first you hadn't trusted him, and barely let him come near you, but eventually you came to trust him. You were a fair way from recovery, but you were getting there.
At the moment you were in a kiddy pool Eridan had set up in the lounge. He had also given you the remote to the TV so you wouldn't get bored. He had to teach you how to use it, since obviously the only electric thing in the ocean are the eels. Eridan was currently out with Feferi, a friend of his he had told you about.
As you were lazily flicking through the channels you hear the door open and close, indicating Eridan's return.
"Hey Er-" ou cut yourself off when you see the state he was in, his cheeks were blotchy and tears were still dripping down his cheeks.
"What's wrong?" you ask in a soft voice.
Eridan sits down on the floor beside your pool.
"Why are people so mean?" he sniffles.
"I dunno." You mumble, pulling Eridan in for a hug, but making sure he didn't get wet.
You lift a hand up and rub your thumbs across his cheeks, wiping away the salty tears. Eridan looks up at you, sniffing once more.
"But I think you're amazing." You chirp.
"Thanks." He replies, the corner of his lips quirking up.
"It's the least I can do." You smile, running your hand through his hair.
~~~
It's been six months since you had been recovering in Eridan's home. You've had pleasant time with Eridan, and you've had so much fun. But today was the day. The day you would return home.
"So, are you ready?" Eridan asks, looking at you as you sat in his arms.
"Yeah." You nod.
Eridan nods sadly before wading into the calm ocean. Once he's about waist deep he lets go of you. You shiver as the salt water chills your skin. You look up at Eridan, who seemed as though he was about to cry.
"I'm gonna miss you." You whimper, tears welling up in your eyes.
"I'm gonna miss you too, guppy." He replies, tears dripping down his cheeks.
You giggle at the nickname. As quickly as you could, you grab Eridan's neck and pull him forward, gently kissing him. Eridan kisses back without hesitation, rubbing away the now falling down your cheeks. You both pull back breathless.
"I'll be back, I promise." You mumble.
You let go of Eridan and swim off into the deep ocean.
"I'll see you again, (y/n)."
