Earlier on, the chapters prevent perma death for the main characters.
The side characters whom you get from quests or the main story-line can be killed
during missions and you can revive them with an item. This item is a finite source.
Once the item is gone forever, you will no longer be able to use that unit. Resulting in perma-death.
Some characters can again only get injured in the beginning and if Felm dies, it's an instant game over.
If you want an updated version of this game where it's a bit easier yet still challenging and has more content and stat changes.
I suggest buying the game right now on steam. Please note it's in early access and a work in progress, but I will not be updating the game here on Itch.io anymore. The demo was for the game jam only. Please have a nice day~