But I just wanted to say this because it reminded me so.
Cute girl that pretends to help the protagonist, only to reveal that she has been only helping you to help her to help her master, only to be killed by her master in the end?
|"Wa-wait! But... that means I will die!?"|
Yeah, deja vu.
That said, you can say Demeter sacrificed herself on her own will and she died for a better cause, compared to that bug's disposal. And hey, Demeter did save your life, so you kinda feel sorry for her.
And yeah, she is loli cute, but no, she does not survive the story in any possibility. Once you unlock her on your second playthrough, have her give a punch to the final-final boss. Closest you'll get. She does have rather... high Power despite her saying that she is weaker than a Pixie.