Ruri

So my guess is this has to do with her powers. Everything with Okarun, Jiji, Vamola, and even her relationship getting better with Seiko all happened after her powers were unlocked. So I have a feeling her memory loss dates back to right before the whole alien thing. So she probably remembers everything up until the day she met Okarun.
The ceremony to get her back to normal again probably conflicted with her powers, maybe even got rid of them and I'm sure it'll become a thing where she needs to reawaken her powers to get her memories back.

Oh oh oh oh!!!! I've been waiting for this day where Jiji and Evil eye work together and Jiji has control of evil eye's powers! But I wasn't expecting the new transformation!
There was a time in this arc where it was feeling a little dicey and slow, but we are picking back up!