Anime with a mysterious lore which is slowly revealed throughout the story?

I have recently caught up to one piece (manga) and made in abyss (anime). While I really like both of these, I also don't like that I have to wait next 5 to 10 years to see how the story concludes.

Which is why I am asking for anime which have an overarching plot based around uncovering the mystery of the lore of the world.

Also, the anime/manga should be completed because I do not want to spend the next 10 years waiting for the story to end.

Any recommendations like this?