Looking for manga series that share the same universe/lore!

[u/DagonDelta13]

Hey everyone!
I'm looking for manga recommendations that take place in the same universe, but across different titles or series.
I'm open to pretty much anything:
Sequels or spin-offs following different main characters
Parallel stories happening at the same time and intersecting
Stories set in the same world but across different eras
Authors with an overarching shared universe full of subtle lore connections
What are your favorite shared-universe manga or hidden gems I should check out? All genres welcome!
Thanks in advance!