HP x PJatO/HoO
"Children of the Underworld to the east you shall go,
To the island of despair.
But careful, beware what awaits you there.
Your worst fears shall you face.
To free the lady of death,
From her chains of grief.
And see her safely returned,
To her home underneath."
Prophecy for the Quest to free the Lady Hari from Azkaban, to Nico Di Angelo, requested by the God Thanatos.
Nico takes Hazel with him (since they are both children of the Underworld), so that would make this story set after the giant wars? Or set just after the second titan war, whenever Nico meets Hazel and becomes Pluto's ambassador.
Other Idea:
Thanatos fines Harry on the brink of death (after series), locked up in her tiny room (either at Private drive or in Azkaban), and gathers up her soul when it departs her mortal shell, and takes it back with him to the underworld. Where he precedes to remake her a perfect body (one without scars or injury, one not cursed with stunted height or malnourishment). There is some help in the process from mother magic: Hecate/Trivia and Harry's many times ancestor Hades/Pluto (he was the father or the Peverell brothers).
Harry is reborn a goddess (maybe her name will be Hariel?), her domains are as such: Death, rebirth, remorse, guilt, grief, bonds, magic, and (familial) love.
And I'm thinking that when she is really deep in some type of negative emotion, her body returns to the sickly one she died as.