AU Sans X Reader One-shots

Cross x Killer's Sister Reader

Requested by JanieRusselltheantic

"Hey, Earth to Cross, snap out of it," Killer said waving his hand in front of Cross' eyesockets.

"You're staring again, it's kinda weird," Killer said once he knew he had his attention. "What do you mean," he asked, obviously trying to lie his way out of it.

"What I mean is you making goo goo eyes at my sister," he replied, annoyance clear in his voice. Cross rolled his eyes at that.

"She's my girlfriend, can't I just admire her," he asked, purposely trying to make Killer mad.

You and Cross had been dating about a month, much to your brothers displeasure. Before you came along, Killer only saw Cross as an acquaintance, but now he could barely stand being in the same room as him.

Killer didn't save you from Chara just to have someone take you away. Course he was just trying to be a good older brother and he wanted you to be happy, but did you have to choose Cross?

But if he didn't save you from Chara then he would've thought he failed as a brother to you. And he was so excited when Nightmare agreed to bring you onto the team.

However, you immediately befriended Cross, not much sooner grew to love him. And as much as he wanted to stop you, Killer let you have your way and you soon got asked out by Cross.

"Ugh, if you're gonna do that make sure I'm not around," Killer growled. "Hey I didn't make you walk into the room," Cross responded, sounding cocky as ever.

"Do you have to do it in one of the main rooms in the castle," Killer asked. "Would you rather it just be me and her alone," Cross was really trying to push his luck here.

"I'd prefer you just stay away from her altogether," Killer answered. "Yeah I don't think that's gonna happen, besides a good brother would just let us be."

Welp, Cross just messed up.

"A good brother would do what he thinks is best for her," Killer barked at him. Alerting you. "And I definitely think you don't deserve her."

"Yeah, well a good brother would let her be happy, and obviously you don't seem to care about that," Cross yelled back at him.

"Both of you shut up," you yelled, silencing them both immediately. "Alright explain, you know how I feel about you two fighting," you demanded, neither would look you in the eyesockets.

"You two were arguing about me again...weren't you," you asked sadly. You hated when they fought, especially if you were the reason.

All you wanted was for the two most important guys in your life to get along. But your brother was a stubborn, overprotective dork and your boyfriend wasn't too far off from that.

Cross reluctantly nodded. "You're not gonna stop, are you," you asked. Neither answered you. You let out an annoyed sigh.

"You two need to grow up already, I know you've both been through a lot but I'd think you cared enough to at least try to get along."

You shot them both an angry look and stomped off. They knew it was best to give you time to cool down.

They just stood there, not even wanting to look at each other. A couple moments later they walked off in different directions, completely avoiding the other.

Cross went off to find a way to apologise to you and Killer needed to calm himself down. But both knew you were right, they should at least learn to hate each other quietly, for your sake.

A few hours passed and he decided he needed to say sorry to you, you didn't deserve them being like that. Yet he wanted to change his mind when he got to your room to see you and Cross sitting on your bed.

"Hey bro. Come here, I need to talk to you," you said, he shook his head. "Nah, I think I'll come ba-." "Shut up and sit down," you barked, he immediately made his way to your bed, not wanting to make you more mad than you were.

"Ok, you two are gonna sort everything out, here and now," you said teleporting to the doorway. You roughly shut the door and held the knob to make sure they didn't try to open it, not that it would've helped.

"Babe, you do realize both of us can just teleport out, right," Cross asked standing up and walking over to the door.

"Yeah, you do and you gotta deal with me," you responded through the door. "Guys, please, for me," you said attempting to guilt trip them, which worked as you no longer felt Cross pushing on the door.

"Get to talking, I'll be here to let you out when you're done," you called before sitting down against the door.

"Y/n, this is ridiculous," Killer groaned loud enough for you to hear. "The sooner you give in, the sooner you can leave," you responded.

"We might as well, she's not gonna forgive us if we don't," Cross said. "Well, what if I don't wanna talk about it," Killer responded.

"And what if I don't wanna talk to you either. We both want her happy though, don't we?"

"...fine. I don't want Y/n with you, not...because of you. I don't want her to date anyone," Killer began.

"Look, when we lost our dad, I had to basically take over caring for her and Papyrus. But then she felt like more of a daughter to me, rather than a sister, which made me more protective of her than I already was."

"Don't get me wrong, I did my best to raise Papyrus too, but there's just something about a little sister that just makes you want to keep her small forever. And when me and Chara made that deal...well I was too late to save Papyrus, I had to make sure she lived."

"I still feel bad I couldn't save them both," he said sadly. Cross sat on the bed next to him, feeling horrible for how he'd been towards him. "Damn man, that's...I had no idea," Cross said sympathetically.

"Anyway, when she told me she liked you I wanted nothing more than to keep her away from you. Not because I didn't want her to be happy, far from that, I just...didn't wanna see her get hurt, not that I think you'd do that, it's just...I don't want her to have to go through that."

"So, what do you have against me," Killer asked. "I don't know, I just...I love her so much, and I know you're just trying to be a good brother but I don't want to lose her "

"I was scared that if you kept talking about how I didn't deserve her, or that she was too good for me that she'd actually realize you were right. I don't deserve her "

"She's the best thing that's ever happened to me, and I don't even want to think what my life would be like if she wasn't in it, even if I've only been with her a month."

"She's the center of my whole world, she has been since the day you introduced us to her. I'm sorry for being such a dumbass, I just...I need her and I can't lose her. She's my everything."

"Look at us, sappy dorks," Killer slightly laughed. "Yep, she's got us wrapped around her finger," Cross joked. "That's for sure."

"I'm sorry too, I know you love her, and I know she loves you. I shouldn't have tried to get in the way," Killer apologized. "I'm no better. So, we good," Cross asked.

"Mostly, yeah. It's just gonna take me awhile to get used to it, it's not easy letting your baby sister go," he answered.

"I'm not gonna steal her from you, and I gotta admit, you're one hell of a brother man," Cross complemented.

They were about to get up and have you let them out when they heard some quiet sniffles from the other side of the door.

They immediately teleported out to see you trying to stop yourself from crying. "Hey, baby it's ok," Cross said kneeling down next to you, Killer doing the same.

You quickly put an arm around each of them, catching them by surprise.

"I love you both," you said, your voice cracking. They both looked at each other and smiled.

"We love you too."