It's hard losing your bestie and crush to evil. Cory knows that first-hand. But this also makes him more determined to get Frisk back. Sure, she's incredibly powerful, and Cory only has humans and creatures with no idea how to bring her back, and Frisk could probably snap them all in half just like that, but hate is no longer power. It's no longer kill or be killed. No, it's love or be alone. And being alone is the worst thing that can happen to anyone. (DISCLAIMER: this is the sequel to Blood, so you better read that first if you haven't already.)