@MeiraEve
More than those two drops of blood coming out of the broken himene, I’d worry more about the birth, there you bleed like a slapped pig... but if the kingdom still exists despite the succession of generations of rose princesses, then probably the "contract" only provides for blood spilled from a wound done offensively by others as an activator. At least I think so.
Who knows, maybe the pact provides that the princess roses are the priestesses of the dragon, and if they are wounded or worse killed the dragon wakes up to avenge them. But because it’s an ancient legend and especially in manga people always do the most stupid thing possible about many possible options, women who should be treated as saintess are instead mistreated and even hated
@Sarsak
scientific moment: what is called menstrual blood is actually not blood, but a mucous membrane created during the reproductive cycle inside the uterus to feed the possible fertilized egg. But if the fertilized egg is not there this mucous membrane deteriorates and detaches from the walls, to be expelled during menstruation. So it had nothing to do with a bleed...