So Ra No Wo To, Made in Abyss Recommendations
Incredible amounts of world building and rich lore is just one similarity Sound of the Sky and Made in Abyss share.
They also share a post-apocalyptic setting; Sound of the Sky takes place after a great world war, and Made in Abyss happens after cataclysmic natural event. After said events occur, the world is forever changed as new civilizations and cultures arise, each with lived-in mythologies and histories.
Thrusting cute/moe characters into this setting is another commonality.
I feel like its the same type of genre, kind of fairy tale-ish (idk how to explain it!!! ><)
but if you liked Made in Abyss you possibly will like Sora no woto!