Comparison: Biggest Anime Mysteries

Unsolved Anime Mysteries! What is the Source of Saitama's Power? What is One piece?
And other to Anime Mysteries like :Why Muzan Spared Nezuko in Demon Slayer? Itachi's Illnes in Naruto? Josuke's Savior in Jojo Bizzare Adventure? Who is Deku's Dad? The original super saiyan, or first Saiyan in Dragon Ball? Origin of titans? What is at the bottom of abyss reg's maker? Dark continent in Hunter x Hunter? What is haruhi? The void century One Piece?
And many more lik Origin of quirks in My Hero Academia? Asta's dad in Black Clover? Black organization in Detective Conan?