Sounds like a Malformed dungeon idea to me.
Except, instead of a church, it's an entire city or town.

Of course, the Malformed are first seen in Harmonia VIII, so far. Jillian's 17 then, so TERMINUS would be two years after (Jillian's 19 in TERMINUS).

Of course, I'm unsure whether to connect Harmonia with ORIGIN and TERMINUS alike, being that they're sorta a Cibryll's Best kinda deal... perhaps it could be but a fleeting dream, or a hallucination brought about by another Malformed... or any other possible ideas that comes to mind. Senbonzakura's awesome. Wait what does that have to do with anything?