Responses
I have come with spoilers about the corpse part, why the boy has aquamarine eyes or what happend between him and MC is a mystery to me.
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MC died of hunger, Winter Spirit brought her back from the dead, which is the taboo he committed.
The boy probably sensed that she was dead at one point and doesn't understand how she's still alive and well.

So he is a corpse that stole jeweled eyes. . . A sort of demon or bakemono zombie? Or is it her? Is it her secondary power or the ice spirit that got her back to life? She isn't a corpse but she did die when she was younger? Did she felt too much bad, sad or wrong energy from the white eyed boy and that's why she fainted? But then, if he isn't a zombie, then does his eyes gots powers too? Like is that why he might have seen something in her eyes?