The guardian dragon is here, and while it's not exactly an ally it's not a definitive enemy either. That the princess of Hugh Jack is becoming a sacrifice as payment for the dragon's protection is news to me; it might've been better if this plot mechanic was explained earlier because Charlotte's actions here seem too sudden, like she already knew what she was supposed to do instead of, y'know, talk with it first.
Or maybe I just forgot and it said somewhere that there was a price to pay for such protection...
The price was always a princess of Hugh Jack, it was explained in the flashback but treated as a fairy tale, they would summon him obviously in the dire time, probably too late or during the attack on their country.
Charlotte has no self esteem whatsoever, from having her family killed in a blood bath and enslavement.
Slow always umbrella protected her, keeping her away from building a character, instead helping her grow whenever she tried to do anything and failed, kept her away from future attempts, this will take a nose dive to anyone confidence.
Her sacrifice is because she thinks she is a burden and useless, so at least there's one way she can help and it's little price to pay in her reasoning.