So I lied and implemented a few shaders and basic colors to the base scene. However I also realized the groundhog day esque mechanic needed to be further elaborated so that multiple different ways could game over and funnel into the scene that Damian keeps rewinding back to. Now the game properly resets and can remember things that carry over between resets. Here's what I mean:
Basically from the Damian scene you can branch out and explore the town to prepare properly for the date. You can start the date any time you want but without certain knowledge that Damian aquires from your past failures or triggering certain events the date will eventually reset back to the Damian scene. Every time you do an event or progress the date, time will forward. Enemies will invade the city prompting you to defend it, but if you're in the middle of the date you will just have to let the city take it. The city isn't gauranteed to be destroyed in a single invasion but if you let too many invasions happen while you're in the date then both you and Singuilera will perish.
So the whole objective of the game is to not only prepare for the date but to make sure the date happens at the right timing. Damian will also let you know when invasions happen the first time you encounter them. I'm wondering if the date could be split into multiple dates as well, like you meet up with Singuilara at certain spots at certain times but that might be complicating it a bit.
I updated with a quick devlog to show how the game works as of now: