Whenever the various musical numbers from the show are referenced there's often a mention of "Heart Song" and "Music of Harmony", the name of the magic behind these spontaneous musical numbers. When and where did these terms get started, though?

Honestly, I couldn't really tell you.

But, like with most memes, they kind of just...happen.

7537251
That's... an interesting question. I'd been wondering that myself -- it seems very common for stories to treat the show's musical numbers as an actual in-universe thing that just... comes into existence now and then as a magical effect, and "heartsong" seems to be the most common name for it, but I have no idea where it comes from.

It's an old word though, I'm sure I've seen it in literature. I believe it's even a last name.

7537251
Likely some fic read by one or another author who reused in in their fic, eventually leading to a chain reaction. But as for finding that original... well, I don't know if it's even possible at this point. (Although you can probably determine the oldest use of it on this site through careful use of the search function.)