so the demons are unable to breathe normal air and has to use gasmasks, interesting.
it is rather odd that they have the technology to make gasmasks but still walk around in loincloths and use spears.
First is when the girl become a witch. This is pretty passive with possibly a slight headache or small fever.
Second is magic Bite (the one depict in this chapter). This is annually and only occur on the anniversary of the respective with's first sign of gaining magic power. This can be fatal for weaker witches (see spoiler note)
Third is (I forgot the term)... coming of age? This is when the magic power "grow" to a more mature form. Anna from normal fire to green fire. This often accommodate with severe pain.
What happening is Roland believe the Magic Bite is actually magic power expansion (of sort). The pain comes from overflowing magic power, so Roland told Anna and Nana to expense their magic power daily.
Technically not really a spoiler. When I said weaker witch I don't mean with's power, but their resistant of sort. This resistant grows as the witch use their power.. becoming more familiar with it .
Some of the initial group who escaped survived (the non-combat types), though some more also died along the way back to their camp
Including Leaf, 7 witches survived out of the 42.
@DrDuckling : The resistance is more mental strength thing. Think of the bites as gaining a sudden surge of magic, and if you haven't been training daily and have low magic capacity, the added magic have nowhere to go and start causing damage instead.
The adulthood one is a special case, where it seems to be the only chance for a witch to gets a secondary ability, if you don't get it on your adulthood, you're unlikely to ever develop one.
You can still upgrade your main ability *coughannacough*