This isn't supposed to hurt.
Genocide runs aren't supposed to hurt, right? They shouldn't make you feel guilty, right? Everyone's done them. It's normal.
You don't understand. Is there something wrong?
Sans continues to talk. You listen. It only makes you feel worse. His words are like knives stabbing into your heart.
You attack again. He looks exhausted. Why are you doing this?
You hate this feeling.
You want it to stop.
You don't want to hurt them anymore. They don't deserve this.
"Ugh... That being said... You, uh, really like swinging that thing around, huh? ...Listen."
You freeze, confused. Scared, even.
"I know you didn't answer me before, but... Somewhere in there. I can feel it. There's a glimmer of a good person inside of you. The memory of someone who once wanted to do the right thing. Someone who, in another time, might have even been... A friend? C'mon, buddy. Do you remember me? Please, if you're listening... Let's forget all of this, okay? Just lay down your weapon and... well, my job will be a lot easier."
Sans is sparing you.
There's hope.
"...You're sparing me? Finally. Buddy. Pal. I know how hard it must be... To make that choice. To go back on everything you've worked up to. I want you to know... I won't let it go to waste... C'mere, pal."
You can't help yourself. You run up to him, wrapping their arms around him in a hug.
'Game Over.'
Of course. What were you thinking? He doesn't even know you exist. He thinks you're Frisk, or even Chara. He doesn't know that they aren't in control.
Frisk and Chara are looking at you with...
...Pity, maybe, in their eyes. You turn away from them, looking at the two buttons in front of you.
...You're going to get them their happy ending.