"Saaaans! Letter for you! It's from Frisk!"

Sans grinned happily from the kitchen. He took a drink of his coffee on the way to the living room and sat on the couch next to Toriel. She was still in her pajamas, so they matched... Then again, Sans seldom changed out of his blue jacket, shorts and slippers, so it was an easy look to adapt to. He looked over her features for a moment while she sorted out the mail. Satisfied, he picked up the envelope and opened it, expecting a friendly 'how-do-you-do' from Frisk.

Toriel sorted out the last of the envelopes before Sans was finished, and she noticed that he wasn't grinning. That couldn't be good. He noticed and glanced up, and held her gaze for a moment.

"Sans, is something wrong?"
"Sort of, Tori. This letter... it's not very nice."

"Not very... Frisk? I don't understand, why would Frisk write you an unkind letter? Did you two have a falling out or something?"

"Not... exactly, Tori... Well, yes and no. It'd be easier to just show you."

He handed her the letter stoically. She adjusted her reading glasses and started:

"Dear Sans,
How are you doing? I hear you and Toriel are living together now. Unfortunate for Asgore, but the two of you seem happy together. I'm happy for you! If you two have kids, I HAVE to see what they look like! Speaking of kids, things have been rather calm since the battle with Asriel. I haven't seen that golden flower that your brother met since, which is a good thing, I suppose.

Sans, I wanted you to know that I haven't been entirely truthful with you this whole time. I'm sure you know that because of my human determination, I was able to reset that entire adventure we all had from the very beginning, when I first fell down into the underground. I also know that that sort of thing bothers you. A lot. More than anyone else, you seem aware of the things that I've done, and I figure there's no point hiding them from you of all people... monsters... skeletons... You know what I mean!

What I mean is, this outcome is the third. This is the second time we all took down Asriel together and went home. But you know about that, right? And the second outcome? Our battle? I don't feel right pretending it never happened. I want to tell you that I didn't kill everyone out of anger, or misery. In fact, it was really hard to cut everyone down with a straight face... Then again, Chara made that a little easier, but the fault is still my own. Those defenseless Froggits, the occasional Temmie, even Papyrus, and Mettaton, and Toriel... I didn't cut them down because I hated any of them. I didn't do it because I was bored, or because I wanted to destroy the world that I had saved out of some sick desire to play god...

When I saved the world the first time, everyone tried so hard to kill me. Toriel fought with her fireballs, Papyrus did his thing with bones, Undyne with her spears, and Muffet? I don't hate spiders, but I don't wanna be THAT close to them! And then there was Mettaton and his bombs, as well as Asgore... He actually fought somewhat like Toriel. Surprising. It ended spectacularly with the battle against Mega Flowey and Asriel, and everyone was so happy!

It was a good long time before I realized something.

I'd seen everyone's power except for yours. Everyone fought with their whole heart to achieve the future they thought they wanted, but you sat back and watched. Curiosity ate me up until I made my decision, and when I did, Flowey and Chara were waiting for me. I started with the toy knife, and I eliminated everyone, and everyone fought even harder to stop me. ESPECIALLY Undyne. She actually had determination of her own, and when I killed her, she refused death! She morphed on the spot and became a lot stronger! But her power was nothing compared to yours, Sans.

Like I said earlier, I had to know what power you were tucking back, what you had to bring to the clash, and you did NOT disappoint. I died more times that I'd like to mention, but eventually, I defeated even you, Sans. I tell you this not exactly as a confession, or an apology, but a simple explanation. I killed everyone because I wanted to see if I'd really gone up against the strongest. Process of elimination, and all. I killed them all because I wanted to motivate YOU. And it was enough to satisfy me. I caught my breath after killing you, SAVED, then went back to the very beginning and saved the world all over again.

I gave everyone back their happy ending in the end, so I say all of this with a clean conscience. Give your brother my regards, and hug Toriel for me.
~Frisk"