I'm happy that you enjoyed the demo :)
There is a story and lore of course, but it's not yet properly represented in the game, which I will try to fix in the future versions.
The purple color is explained by this rat itself - you just need to keep talking to them :)
As for the combat, I totally agree, and actually some of the additional combat mechanics, like "vengeful spirit-like" magic shot, setting explosive and throwing grenades, are already implemented - but they are supposed to be obtained later in the game.
Thanks a lot for your feedback!