The "Conversion" sidequest. Rosch acts like Sonja has a carving knife in her hand every time you find a Core Part:
Sonja: Oh! Core Parts! Now I can strengthen Rosch's Gauntlet! Are you ready, Rosch? Rosch: *!* H-Hey! What are you trying to do!? I don't like that look in your eyes... Sonja: *"music note" emote* Heh... Don't worry. It won't hurt! Rosch: Er, Sonja... Calm down. Let's talk this over... Sonja: No! *screen fades to black; sounds of working and battle* Sonja: You look quite dashing, Rosch. Rosch: *"grumble" emote* I thought I was going to die... Sonja: If you find any more parts, you know where to bring them! Rosch: Ugh... Please don't find any more parts. Sonja: ...What was that, Rosch? Rosch: I just said I'm so reli...Er, no. I'm so re--Um, let's go, Stocke!I can't wait to test out all the new powers of my Gauntlet!