In the second part, Loki's been murdered and Thor sets out on an epic quest to find his soul and get it back. The fic ends in Ragnarök happening right after Thor has actually got Loki to remember who he is (since he'd lost his memory of his life in Valhalla) but the ending is still happy.
Anyone remember this one? Feeling a bit desperate rn since this ship is kind of huge... thanks in advance for an help! :'3
EDIT: made one more last ditch attempt to use a3o tags fu to locate fics and did... at which point it turned out I did have them bookmarked after all??? That's what one gets when looking for fics while sick I guess. Sorry for the trouble!
The Song Unsung and the Broken Saga by khaleesian.