The Creation. (UndertaleAU Sanses x Female! Creation! Experiment! Reader)

Treated like his own

Don't play the song until the fight further in the chapter. Plus, I'm using Chesstale Sans's theme because it sorta fits in with the battle .-.
☝︎♋︎⬧︎⧫︎♏︎❒ (Gaster)︎ P.O.V
It has only been a week since I had Y/N held in my lab. And for a strange reason, I had been treating her as if she was like a daughter to me. I gave her a room, I fed her nice food, I even let her go shopping. I have taught her a few new things throughout the full week and it puzzles me that I am acting like a parent. "Gaster?" I was snapped out of my thoughts and was met by Y/N looking at me. We were having breakfast right now. She had a bit of worry and confusion on her face. "Are you ok, Gaster?" I nod my head and smile. "I'm fine, Y/N" I respond. She looks down and her smile soon faded. "Gaster?" I hummed, gesturing her to keep talking. "I miss my friends...the Sanses, y'know?" I look at her, and saw how unhappy she felt. I sigh and give her a smile. "I never should've taken you away from them. And I never should've corrupted your soul." I put out my hand, her F/C soul appears in front of her. I put my hand to a fist and a black, gooey substance came out of it. I placed the substance in a vile and held it in my pocket. "Come." I got up and held my hand out. She looked confused but took it. I teleported us in the forest close to the Sanses house. "Your friend's house is a 5 minute walk down north. You are free to go, but don't come and visit..." she looks at me with a smile and then tugged my arm. "Come with me. I want you to live with us..you've been like a father to me. You have acted like my Papa..so please...stay?" She had hope in her eyes and I sigh. "Alright. I'll give it a try." We walk to the house and Y/N happily knocked on the door. Reaper opened it and his eyes widen. I gave a sigh and smile at him with Y/N. "hello, Reaper." Reaper summoned a Gaster Blaster and was attempting to shoot me. Y/N got in the way and blocked the attack. "Reaper, it's fine. He's with me" Reaper nod and let us in. She went to explain to the others and they happily accepted me into the group. She gave me a room in the guest room area. I smiled at her. That night, I got Y/N to sleep with one of my childhood lullabies. She sighed and got to sleep easily. I went to my new bedroom and went to sleep. I, somehow, felt..happiness.

Classic P.O.V
I woke up the next morning after Y/N came home. I'm surprised that Gaster had a soft spot. I was just talking to him until I had to excuse myself to the kitchen. I went to the fridge and got a bottle of ketchup. I walked back to Gaster and saw him sitting on the couch with his phone. He was talking over it. I look at him. He saw me then went up the stairs, probably to his room. I sat on the couch to watch TV until I heard a scream. It sounded like Y/N. I ran upstairs to see Night,are, Gaster, and Y/N in her room. Y/N was behind Gaster and he was looking as if he was trying to protect Y/N. Nightmare soon turned around and his smirk grew wider. "WeLl. ThE ClAsSiC DeCiDeD To BuT In." He says. My left eye went blue, I summon a Gaster Blaster and shot Nightmare out the window. He landed with a hard crash and the other Sanses came rushing out. "Gaster, take Y/N somewhere safe. We'll take care of him."   Y/N looks to me. It got me confused, she smiled and Gaster nodded to her. She jumps out the window and confronts Nightmare. My eyes widen as Nightmare smirks. Y/N's smirk seemed to grow wider. She summoned one of her Blasters. It looked different from the last time I saw her using it.

Y/N P.O.V
"Tonight will be a beautiful night.." I said. "People will sleep as the stars come out..." I chuckled darkly and took a few steps forward, Nightmare somehow took a few steps back, which shocked him, and satisfied me..heh well..almost. "Heh...but..." I say, closing my eyes and gave another dark chuckle. "That night will only be beautiful..." I open my eyes, revealing the, to be empty, black sockets. "If YoU WeRe DeAd WhErE YoU StAnD!!" My left eye flashed F/C and S/F/C and my grin grew wider. Nightmare used one of his tentacle to grab me, but I grab it instead. He looked shocked. I pull his tentacle and he comes flying at me. I grab him by the jacket and smirk. I manage to throw him up and a Blaster shoots at him. He hit a tree. He looks at me as if I was a Nightmare to him. Then I saw something that caught me off guard. I saw my creator standing there in the place Nightmare was standing. My eyes went back to pinpricks and I stare at my creator as he had blood stains on his nice white lab coat. "Y/N. Come. Let's go home." He says. I was at the verge of tears. My creator held his hand out. I took a step back. My creator soon turned to dust and Nightmare hits me with a tentacle. I became shocked at the sudden verge of it. I hit the wall of the house. I stood up then looked to my hand. It was covered in blood. "Heh....that was....unexpected.." I had sweat on my skull. I sigh. "I guess I have one more thing in hand. But I get bone tired after that..." I closed my eyes then open them up again. My eye flickered F/C and S/F/C. My left eye was covered in a F/C flame. Nightmare looked shocked. I lift my hand and his soul appears from his chest. I raise my hand higher and he starts to float. Out of the sudden, a large bone appears and it pierces through him. His eyes widen and my grin grew wider. Four sharp bones pierce through him, then I drop my hand, letting Nightmare hit the ground in a large crash. I summon the biggest Blaster I made. Looks more 2x the size as my regular ones. And attempt to shoot Nightmare, but something popped up.

~flashback~
"Papa, look!" Your creator rushes into your room to see you on your bed, a spider was standing on the floor. "W-what is that!? Kill it, Papa! Kill it!" Little you shouts. Your creator picks the spider up. "Now, now, Subject 1. A spider like this won't harm you. And you shouldn't really kill a living soul." Your creator says. He walks to you and gestures you put out your hands. You did so and he let the spider crawl on your hands. You smile happily at it. "You must learn to show mercy to all living creatures. Especially the bad people." You nod your head and pet the spider before placing it on your window cil. The spider crawled away and you close your window.

~end of flashback~

"No!" My Blaster was shot but it missed Nightmare. He looked at me with a confused look. "My creator said: that I have to show mercy to all living creatures when I was a baby bone. Especially those with a corrupted soul!" I exclaimed as I walk towards Nightmare. I was pretty tired after using my special attack. I knelt I front of Nightmare and he looked confused as ever. "So.." Two buttons appear in front of me.
[fight] 💙 [mercy]
[fight]  💙[mercy]
I clicked on the mercy button and spared Nightmare. I stood up and smiled as I walk off back into the house, leaving Nightmare to teleport away. I look to everyone, already knowing what they were gonna say. They would ask why I spared him, and that's exactly what I heard. "Kiddo." Classic looks to me. He had a bit of shock on his face. "Why did you show mercy to Nightmare? He could've killed you!" I look at him with a sigh and a smile. "Because I know that everyone deserves mercy. C'mon, Classic. Even the bad people can be good....if they just....try" I said in response. I walk to the stairs as an axe hit the banister. I look behind and saw all the Sanses looking at me with either confusion, worry, or sadness. I sigh once more. "Everyone. Deserves. Mercy." I said to them. "I'm gonna go fix my bedroom window now. Let me know when dinner is ready.." I walk up the stairs and into my room.