The player will be able to "romance" most if not all of the girls in the castle. Not really sure what you mean by "option to stay and the option to leave", regardless I don't think I should answer that in case I spoil anything.
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The description says you can either escape or fight the demon, doesn't that mean escaping means leaving and fighting means staying?
Falling in love with multiple girls doesn't mean it's a Harem, so I asked if he would have a Harem, or would he have to choose one of the girls?
My English is not very good, I hope I was understood.