Responses
It was Eleana's sister who sang it to sloth before he killed her (why he said he heard it it before but sung not well). That was mentioned in the last 3 chapers. Sloth's wife been dead for a while that's why he's been asleep for a long time
I agree with everyone that this is a slow read. I can live with that, but I see that being a major turn off for some people.
Now with that out of the way, Elliana's music instructor is probably Sloth's wife.
I don't know how, but considering that two of them know that tune, that could be the only connection.
And after figuring that out, they find out that his wife is doing okay and she has learned to live with her immortality, which is gonna help our stupid couple with the "growing old" part of their worries... So another 80 chapters probably