Merfolk's Lullaby

(Something is carved here. You're not sure how, but you can understand its meaning...)

Then came the day I saw the ship and heard again your distant cry, I reach, and snared it in my grip. At last, our chance to say goodbye. Yet fate is crueller than the sea. Your soul so close, but locked away. I made my oath. 'Til you are free, all those who walk above shall pay.