The
proper response of Hinako would be to decline with an explanation that she's already declined an invitation from Miko.
At this point, the story conforms well to
@Benjansss's
#3 and to
my #4.
@farrel160704—
I bet that the Childhood friend is also a monster...
That's a real possibility. But, again, the Japanese are very big on imputing significance to homophony, and that friend's name is “
Miko”. So, if she is not a protectrix for Hinako, Miko is more like to be
in the service of a divine monster than herself to literally
be a monster.