Monsters being selfish is an interesting reflection on Miko. She wants to protect Hinako and help her. Though it is rooted in her friendship. Of course what Hinako wants, she could never give to her. I mean, letting your friend die—who would give them that? Miko resembles much more a human than a monster.
Though Shiori sounds cold about everything, she does it for herself. Though the scene where she sees Hinako’s scars and gets her to be able to take a bath away from her classmates. Shows she is not as selfish as she states.
The idea of dead humans becoming monsters is interesting. Then adding Hinako’s scars adds a layer. Even more so, Hinako finally sees Shiori’s monster form fully to add moreover.