I think she is in the past way before the novel happens and she is somewhat related to niella
That's possible. Maybe Aikal met Katisha inside the demon sword.
Maybe Aikal confronted Niella because he got suspicious of how similar Niella's life with Katisha's.
Maybe Niella did something bad to obtain the heroine role?
Or maybe that Aikal was from Katisha's timeline.
We also still didn't see Yeoju, the other adopted daughter aside from Niella.
That girl was mentioned in chapter 2.