Hi! If that's okay, x reader headcanons with Muffet, Mettaton and Grillby where the reader is sensitive and a bit overly empathetic?
Undertale!Muffet - You might actually unlock Muffet's softer side. Yes, despite her seemingly violent and greedy outer shell, she actually is a very gentle soul on the inside -- she is merely doing what she needs to to survive. Anyone who would be even remotely sympathetic for spiders would earn Muffet's trust, but to be empathetic is on a whole different level. It wouldn't be unreasonable to assume someone like this would make a donation or few to Muffet's bake sale, despite the prices, and a repeat customer who doesn't seem upset after spending their money is enough to leave her intrigued.
Undertale!Mettaton - You would remind him of Blooky, all things considered, although empathy is not necessarily wholly negative like most of Blooky's emotes tend to be. Mettaton would honestly find great interest in you and he'd actually more often than not find himself opening up around you without even realizing. Despite being so loud and proud on stage, Mettaton would be rather gentle and quiet around you, and probably be rather careful of your sensative boundaries without even realizing it.
Undertale!Grillby - All things considered, Grillby is the least prepared to handle someone like this. He won't really visually -- or verbally -- show it, but in actuality he'd be a little overwhelmed. In a good way or bad way? Even he's not really sure. But he enjoys your company, that much is certain. If you go talking to him enough, he might even start picking up on even the littlest of things that make you upset or uncomfortable and avoid them like the plague. He recognizes that you're always rather emotional, but he makes it a goal for all of those emotions to be something you can smile about at the end of the day.