A/N – I don't own Fire Emblem Three Houses and Resident Evil. Before I go into the story, this is an Resident Evil AU, not quite a crossover, so it will have a few resident evil references, but not a lot because I only know the important bits.

It will be a Female Byleth X Dimitri fic because I'm a shipper, and yes, I ship Male Byleth X Dimitri as well since they're technically the same thing, just yaoi (Not the biggest yaoi fan. Just only a fan of a few). Also, I pick female over male because Resident evil tend to have one male protagonist and one female protagonist, so that's why.

Also, Byleth will be a bit OOC, but that's to be expected in a AU. She will have a no nonsense, calm and quiet personality in here like in the game, but she'll be a bit more expressive and such since she's just a normal mercenary being here.

Without further ado, Enjoy!

In the dark, starry night where a helicopter is flying through the ocean. Inside of the helicopter is a male pilot riding it and on the backseat is a young woman with dark aqua hair, purple eyes and pale skin. She wears a black tank top that shows a bit of her midriff, a brown jacket with rolled up sleeves, fingerless gloves, brown sash for her guns, black tight jeans, a backpack and military boots.

She stares outside of her window, where she thinks back to her client...

(Flashback)

The woman sat on a couch inside of a nice looking room where a man with wavy dark blue hair, pale skin and blue eyes entered in.

"Mr Fraldarius, correct?" The woman asked.

"Please, just call me Rodrigue," The man told her as he sat down on his desk. "And you must be Byleth Eisner, correct?"

"Yes. I am," Byleth replied.

"Good," Rodrigue smiled, "Now, I'm sure you know the basic of this request I will give you, right?"

"You want me to go on a rescue mission, correct?" Byleth replied.

"Exactly." Rodrigue nodded as he showed two pictures to Byleth, "I want you to rescue those two."

Byleth took the pictures from Rodrigue and gotten a better look at it. The pictures have a teenage boy and a girl, both around the same age, which they looked around their late teens. The boy have a handsome face with gentle blue eyes and neatly done blonde hair, while the girl has a beautiful face with lilac eyes and long, brown hair with purple ribbons on each side of her hair.

"Those children are named Dimitri Blaiddyd, and Edelgard Von Hresvelg," Rodrigue told her, "I'm sure you heard of them from the news."

"They're... they're part of the royal families..." Byleth said.

She was well aware of the royal families. The Blaiddyd bloodline ruled over a small kingdom of Faerghus, that is centred around the north of Russia, which was where she's in right at that moment. The Von Hresvelg ruled over the Adestrian empire, that is located between Germany and Austria.

However, a couple of years ago, the king of the empire died of cancer and the queen of the empire married the king of Faerghus after his wife died of childbirth, making Edelgard and Dimitri step siblings.

Unfortunately, the marriage between them didn't last as the new couple suddenly got assassinated, by a mysterious figure. Nobody knows who did it and their deaths has been part of a conspiracy theories for years.

"And you know what's happening to them?" Rodrigue asked her.

"They suddenly gone missing," Byleth said, "And you hired me to go look for them, correct?"

"Yes." Rodrigue told her, "And you'll be rewarded with a blank check; anything you would want."

"... Very well, then," Byleth said as she gets up. "When do I start?"

(Flashback ends)

Byleth sighs, where ever since she accepted that request, she's been looking for them for days, weeks, almost for two months tirelessly. However, she finally found her targeted location... she hopes; a small, abandoned island called Shambhala located around the infamous Bermuda Triangle. Though, she doesn't know why those two are there, but there's possibly more to the story than she thinks.

She's never been a woman of the supernatural, so she doesn't believe in stuff like that. Though, a few pilots denied her request, thankfully one is brave enough to go with her.

Suddenly, the area starts to get foggy and harder to see, which the pilot groans and swears, "Fuck! It's getting pretty damn foggy here,"

"No shit, Sherlock," Byleth replied.

"We have no choice, but to lower down to sea level," The pilot told her.

"Got it." Byleth replied.

Just as the helicopter lowers down a bit, the mercenary hears a strange noise outside and just when she turns around, she spots a missile heading their way. She quickly grabs a hold of the controller, where the pilot shouts, "What the fuck are you doing?!"

The helicopter moves to the side where the missile only hits the main rotor blade, causing the helicopter to spin around crazily.

"A-AAAHHHHH!" The pilot and Byleth screamed as they were spinning around the helicopter.

The helicopter crashes to the edge of the island, causing massive explosion. Byleth flies off from the helicopter and rolls around the sandy floor. Some of her clothes are burnt a bit, she has a burnt arm and a nasty scar on her shoulder from a shard of glass. She slowly glances at the pilot, where he has an even worse luck than her.

The pilot is closer to the exploded helicopter, and laying on a pool of blood as a shard of glass stabs through his back.

"Shit... he's dead..." Byleth thought, and than, the helicopter explodes again with the pilot in it. "Yep... totally dead..."

She weakly gets up and turns around slowly as she sees a massive futuristic looking building which is a massive sore thump compared to the dreadful and abandoned area surrounding it. The sea close to the island is dangerous polluted, the plants looks dead and feel very abandoned.

"And yet... there's a building here, of all places..." Byleth thought, "This is very suspicious obviously... I have no doubt that I'm heading at the right direction..."

Just as she moves a bit, she gasps in pain, "I... I need to do something about my injuries... it's a miracle I didn't get knocked out... lucky me..." She thinks as she rolls her eyes.

She takes out her backpack and takes out some medical materials just in case. She always been told a good mercenary must be prepared at all times, that's what her father taught her... before he disappeared mysteriously.

"No... focus on your mission, Byleth..." Byleth thought as she starts tending to her wounds, and slowly, but firmly takes out the shard from her shoulder, "Fuck!"

A massive pile of blood drips out from her shoulder and drops the shard on the floor. She starts tending to her wounds with her supplies; relief that she taken the supplies just in case.

(Meanwhile)

"Mmm..."

A young boy, around 17-18, with slightly messy, blonde hair with a tint of white on his bangs, pale skin with stitched scars on his stomach and chest. He only wears dark blue trousers and dirty trainers, showing his slim, yet well built body. He slowly opens his eyes, revealing his left red eye and his right blue eye. That boy... is Dimitri Blaiddyd, the prince of Faerghus.

He glances around the room, where he's in a prison cell with a broken mirror and a messy sink. He groans as he gets up and looks at the mirror, where he notices the tint of white hair and red eye, which his face turns pale and hugs himself.

"I... I look like a freak..." Dimitri muttered, "I... I have to get out of here! I have to! I want to go home, damn it!"

He looks around his cell. Unfortunately, there's no windows to break through and only the exit he think of is through the front cell. He takes a deep breath as he tries to pull out the cell's bar... which he did effortlessly.

His eyes widen in shock of the fact he now has super strength, which, while it makes him feel even more of a freak, would be super useful in his escape. He decides to quietly put down the cell bar to avoid alerting his kidnappers, and runs out of his prison cell.

"Now, to find Edelgard and get out of here!" Dimitri thought.

He tip-toes his way out of his cell, being very careful in his escape and not wanting to grab his kidnappers' attention. Just as he walks to the end of the prison's hallway, he grabs the knob of the door and just as he opens up...

"OH SHIT!" Dimitri swore as he quickly backs off as something tries to grab him.

"Ugh..." Something moaned. That something is a zombie with disgustingly pale skin with a tint of green, stitches all over it's body, pure white eyes with no pupils, a glowing red thing on the right side of it's chest and bloody, black hair. It wears a bloody black tank top and jeans as he tries to grab Dimitri.

Luckily, it's very slow, so just as he is about to move past it, the zombie suddenly grabs onto and surprisingly, has a very strong grip onto him as it is about to bite down his throat. The prince manages to push it away from him and out of instinct, rip it's heart from the host. The heart has a strange red stone attached to it.

Dimitri smashes the heart with his bare hands, which the zombie collapses to the floor while the stone stops glowing. He drops the smashed heart to the floor and carefully takes the tank top from the corpse.

"It's dirty and smelly... but it's better than walking around shirtless where those freaks can easily bite me," Dimitri thought as he puts it on. "Now, I need to find some sort of weapon in order to defend myself from those freaks."

Dimitri walks out from the hallway, unknowingly being watched from the sidelines by a camera.

On the screen where it shows Dimitri escaping, a man with deathly pale skin, white beard and white eyes is watching the screen with a smirk as he mutters, "... It's time..."

A/N – I tried to make it suspenseful and intense. I'm quite terrible at the horror genre, so instead I tried to make it feel suspenseful and fun.

You could say Byleth and Dimitri are a bit similar to Leon and Ashley, except Dimitri is WAY less annoying, very capable of defending himself and stronger that will be explained more later while Byleth is agile, slightly weaker and more straight laced compared to Leon.

Anyways, I hope you guys enjoyed this. Have a good day! Aqua out!