I was wondering if Uboa's looks could be explained with this: Poniko was Madotsuki's friend, yes, and maybe poniko killed her self, or something... her face might have been deformed and twitched, and maybe she was dead in her own room, while the door closed... maybe madotsuki went to pay a visit for her "sick" mate or something.. and poniko's parents ought that she was just staying in her room quietly... after madotsuki went into the room, everything was dark and she discovered her friend laying on the floor, dead for few days and the dead disfigured face? And that's why uboa appears only in the dark?
How would poniko's parents not go into her room, or look for her for days? But other than that, I believe this theory has already been done. Or something like it.