whenever i think of this pairing, i think of the song Gentle Jena from Planetarian: The Reverie of a Little Planet. Ever since I played through Planetarian, I ended up associating that song with Mettafrisk for some reason. It’s kind of become my little headcanon song for them. Not really sure why…perhaps its because Planetarian is about a human and a robot developing a bond, and Mettafrisk is also about a human and a robot (ghost) developing a bond, too.
Either way, it’s such a beautiful and heartfelt little song and I love the thought of Mettaton and Frisk slow dancing to it, haha