Yandere!Under verse x Reader

Waking Up

Memory: Don't worry Kiddo, I'll explain everything to you, okay?

Y/n nods, looking at him in curiosity and knowing they can trust him without knowing how they know they can trust him.

Memory: Well, as I said before, my name is Memory!Sans, and I come from the au, Memorytale. Au stands for Alternate Universe, like this one and Memorytale. We all come from the original universe, Undertale, but certain circumstances make us change...or in simple terms, an au happens because a change happens in the original, be it in the past or future.

Y/n nods slowly, rubbing their eyes tiredly, still wanting to sleep. Memory chuckles.

Memory: I know you want to sleep, Kiddo, but you can't at the moment. So, what's your name?

Y/n, yawning: I-i'm Y/n...it's nice to meet you Memory.

Memory, nodding: nice to meet you as well...now how about we get out of this au, and find you someplace to stay?

Y/n, now abit distressed: but my brothers! I gotta find my brothers!

Memory blinks slowly, taking in the information.

Memory: brothers?

Y/n, nodding: mhm! Their names are Dream and Nightmare!

Memory, slowly: Well, I recognize one of those names, but I don't know the other. Who is Dream?

Y/n: Dream is my younger brother! He's the guardian of positivity!

Memory: well waddya know...there is a guardian of positivity...but if those two are your brothers, doesn't that mean that you're also a guardian?

Memory asks that last question with a raised brow as Y/n nods, their wings flapping in distress.

Y/n: Y-yeah! I'm the guardian of memories!

Memory, now confused: but I thought I was the guardian of memories...well, we can have two guardians I guess...but if you are a guardian, the best thing for you to do right now is learn how to use your powers physically...I know you've been using them mentally, that's how I was able to find you.

Y/n nods, looking at the skeleton with teary eyes and a puppy dog look that they had mastered from Dream. Memory sighs and runs a hand over his face.

Memory, sighing: alright, I'll help you look for 'em, but I'm also helping ya with yer powers kiddo...but you might not like what you see when you see Nightmare again, and I don't know where Dream is, but we can search for him, okay?

Y/n nods, completely fine with this. Memory stands up and extends his hand towards Y/n. Y/n takes his hand with no hesitation, determined to find their brothers.

Memory, sighing: I hate work, but I do gotta help ya...Besides, Yagi(Toriel) will be able to help you as well, same with the kids.

Y/n nods and Memory makes a portal out of ice, similar to the ones Y/n can do, but also noticeably different. Memory walks through it, with Y/n following. The two appear in Memorytale, in a plaza. Y/n looks around, and lets out a breath they didn't know they were holding. This place, Memorytale, feels like home. It feels like they came home after years..

(A/n: multiple timeskip warning)

~~timeskip of 10 years~~

A/n: Y/n is 18 now physically, but 276 in total, counting the years they were asleep and didn't age.
~~~~

So, as it turns out, Y/n is the original guardian of memories, but their disappearance, aka them falling asleep for 250 years, caused Memory to become the new guardian of memories. You two didn't really mind this, and actually got along pretty well. You also did get along well with Memory's adopted kids, Hope and Willow, with them becoming your siblings and Memory being your adopted father. At the current moment, you are in a forest, walking with Memory.