you fall down with Clover into the underground to see what happened to 5 missing kids and where they went

you both kill dozens of monsters on the with Flowey helping you load, you both kill him and Martlet too, you both reach Asgore (the dude who unwillingly killed the kids)

Asgore: …you have ensured one thing… this war shall never end due to your violence…

But even if you chose differently…

Your fate was sealed the moment you entered my kingdom…

Clover: “Shut up already.”