Maybe some lore buffs can help me out here. Sivir's lore states that whatever was in the tomb "set... events in motion that would change not just Sivir's life, but all of Shurima forever."
I've always assumed that this was either the tomb of Xerath or some trigger that summoned Nasus and Renekton. However, doesn't it make much more sense that this was the tomb of the ancient emperor?
Theory Xerath hungry for power, starts a coup with Renekton against Azir. They successfully subdue the emperor but are later imprisoned by the still loyal Nasus.
Fast forward to present day, Cassio hears about this ascension business from a released Xerath and Renekton. Goes to the tomb with Sivir for clues / tools to achieve ascension but mistakenly revive the long slumbering emperor.
The emperor isn't happy about his empire being lost, he discovers Cass wants ascension for herself and puts a curse on her. Sivir on the other hand, probably reminds Azir of someone from his time (presumably some loyal mortal reincarnated).
Plot Twist Nasus and Renekton are not related to Azir by blood but are of the same race.
Amumu is Azir's mummified son.
