Mind spilling the beans then, since the arc basically got skipped?
So the last saint before Elrise was Alexia.
When the Saint kills the Witch, the curse is transferred to them, and they go through a terrible transformation and become the next Witch.
Saint Lilia was the Saint from the generation before Alexia. She was one of the weaker saints, and struggled in her battles against darkness. She was raised from birth to be the saint. She never had a life of her own to live. She only one purpose. To be the saint. She resented her fate but never gave up and did her best anyway.
She died after being attacked by monsters although it was implied that she did so intentionally; aka that she comitted suicide. She most likely killed herself because Aiz told her the truth...aka, even if she could kill the Witch, she would become the next Witch.
Who could do their duty knowing that would be the outcome? Lilia couldn't bare that burden. So she decided to die instead. She took the easy way out. But who can really blame her?
When she died, the Witch of that era had no further obstructions and wiped out most of the human territories with little resistance. Tens of Millions of people died before Saint Alexia could be born and grow up and finally kill the Witch who by that time had been loose on the world for almost 40 years. ☠️☠️☠️
Tragic. 🥺