Undertale /au's x reader 6.

Devil within. (Special)

Finally an update? Yeah. Idk I got the idea when I drew a little something.

Basically my own personal headcannon as of why Blueberry is psycho.

Enjoy ~

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It all started with an ache.. An ache of a twist in his nonexistent stomach.

The way other monsters looked at her, the way his older brother stared at her.. It made him sick. Grit his teeth in anger.

He thought it was just jealousy, which is why he stole her attention from others. Jumping in on her conversations in front of other monsters.

But.. No matter how he tried to ignore it.. It kept coming back. Haunting his dreams.

He would have dreams of them together, in waterfall, in the wishing room, sharing stories of her surface life.

Holding hands.

Before he could even mutter a word to her, someone would always rip her away from him. Leaving him in the cold with a aching heart.

He would always wake up gritting his teeth, always in a cold sweat, gripping his sheets tightly with his fists.

The dream catchers failed to keep the nightmares away.... Again.

"Please.. Stop this! What do I have to do to get rid of this!?" He would scream, clutching the sides of his head.

"I can take your pain away from you.. You just have to listen to what I have to say." A voice would whisper to him, its form appearing in front of him.

"Who.. Who are you?" The small skeleton asked, flinching away from the monster clad in white.

It seemed to be a skeleton much like him, taller of course, dressed in white.. Soft wings behind them.

"Your guardian angel of course." They smiled, arms behind their back, showing no harm.

The blueberry tilted his head. "Guardian angel?"

They nod with a soft smile.

"Can.. Can anyone else see you?" He asks, slowly making his way over to the angel.

"I'm afraid not. You are the only one who can see and hear me.. Now.. Listen my dear, I have many things to teach you." They smile.

However it was fake, hiding true malice.

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The Blueberry had taken the wisdom from his guardian angel, knowing they would never lie to him.

The dreams were insecurities of losing the human girl he had grown to admire..

The angel had said do what it takes to keep her close.. Win her over so she sees no one else but him.

All was going well, she came over more often than usual, watching Nabstabot's newest drama with him. Cooking with him and she even bought him a new bandanna with stars on it!

He never took it off since her smooth fingers graced his neck to tie it into a neat bow.

Yes all was well until..

Alphys had attacked her in waterfall just for passing through to see flowey village.

His brother had carried her wounded body back to his home, her sleeping form was upon his bed, covered in bandages.

Little blue felt rage.. How dare she? Alphys attacked her without reason!? How dare she hurt his darling!?

He pattered back and forth in his room, trying not to wake his darling with his low growling.

"My dear... What seems to be troubling you?" His angel asked, appearing at his desk, it's hands cupped together.

Little Blue turned to the angel, eye twitching. "Isn't it obvious!? Look what Alphys did to her! I wasn't there to protect her!"

The angel did not reply for some time, it was hard to tell their expression thanks to that cloth they wore over their eyes.

"I can't just let her get away with that!" Blue clutches the sides of his skull, closing his sockets tightly.

The angel suddenly smiled. "Why don't you punish her? Get revenge for what she did to your beloved?"

Little Blue drops his hands in his lap then looks up at the smirking angel. "I can't just hurt her! That'd be wrong!"

The angel suddenly appears behind him, their warm hand on his shoulder. "But think of all the pain your darling has went through, look at her." The angel turns his chin so he can look at the injured girl on the bed.

"She did that to her, you just know she enjoyed it. What's going to stop her from doing it again?" The angel whispered, right next to his face.

Blue felt a sudden rage take over him, he looked over at his desk, a locked box sat upon it. The key around his neck.

"Go on... Show me what you can do.~" The angel grins. The box levitating over and plopping into his lap.

The latch breaks as the lid opens.

A silver blade laid upon the velvet carpeting inside the box, it gleamed in the light of the room.

A white bow wrapped around its handle.. Holding it.. It felt like it was made for him to hold it.

A smirk stretched on his face.

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Not long after Alphys, many other monsters began to disappear, seeming to drop like flies..

Little Blue's left eye began to glow a vibrant scarlet the other being baby blue with a heart pupil.

His boots clicked against the golden hall's tiled flooring, the sunlight came through the windows of the barrier.

"So, you've been busy...huh? Welp.. Sorry old man.. This is why I never make promises." The voice of his brother announced, turning to face the human girl.

However.. She wasn't there. His younger brother slowly walked towards him.

"Wait.. Sans.. What are you doing here? I thought I told you to stay home! It isn't safe.. C'mon were taking a short cut---"

"There will be no need for that..." Little Blue spoke with malice.. Voice dripping with venom.

"What? But the human, shes on her way to ki--"

"Kill us? Why would she ever do that? You know she wouldn't even insult a froggit. What makes you think she would hurt us?" He giggles.

The judge looked over his brother. His eyes widen as he felt his soul stop.

Sans.

Attack: 38 (99)

Defence: 4 (99)

Lv.20.

HP: 99/99

Exp: 999999

Kills: 111.

"S-sans.. What did you do!?" The judge yells, backing away from the small skeleton.

"He only did what I told him to." A chilling voice giggles, a figure appeared behind his brother, it clad in white, pink wings spread out behind it. Horns upon its skull as it tilted its head with a sickening smirk.

"What the hell..." The judge shakes, cold sweat going down the side of his skull.

The angel grins wider and extends its arm, holding a silver and magenta blade.

Blue did the same with his, both eyes turning a bloody shade of red as his grin widened in madness.

"Come my pet, let us show him what you can really do.~" It cackles.

Little blue only nods as he raises his blade, many dragon like skulls appearing behind him as his eye lights went out.

It was no angel after all.