Adding to this, the concept of demons being able to just make people disappear like they do in the movie is terrifying to anyone but especially to a kid. They spend training tormented by nightmares of being completely forgotten and erased.
I always headcanon that Celine kind of stepped up as a surrogate mother for Mira and Zoey but especially for Mira (She sees some her own anger in her from before grief and time wore her down) post idol award Mira can barely stand her. The first time they speak is mostly Mira completely tearing her apart because she was who Mira went to sobbing as a kid because she was so tired of being so angry all of the time, she was the first adult to even try to nurture her, she was the one listening when Mira came to her terrified of how she felt for her bandmates.
But she was also the one who got them into this. Who exposed them to the horrors of their world. She held Mira while she cried about loving Rumi, but turned around and told that same Rumi to hide from her. The betrayal's so strong Mira can't bring herself to even look at Celine for months after that.