What a surprising and excellent story this turned out to be! Its dark atmosphere and plot would lead one to think it's horror, but instead it proves to be so hopeful.
There's a beautiful story of companionship and mutual trust and care between a cursed monster, a human victim of a mysterious plague that's split the world between the Outsiders (creatures of Darkness) and the Insiders (of the Light), and a girl child abandoned in the cursed woods who for some reason doesn't seem to transform due to the curse. Although there's "Beauty and the Beast" undertones in this manga fairy tale, the relationship between Teacher and Shiva isn't romantic, probably because Shiva is still so small. She's appropriately naïve and trusting as a child her age would be, but also extremely resilient, and for a monster he's quite the caring sort. Their story starts with their relationship and a few other things already established though not yet elaborated on, a little as in media res, and the plot moves at a slow pace and the mysteries tend to be unravelled very slowly as well, which will require patience so as to not feel frustrated too early and be rewarded as the story progresses.