you don't permenantly lose the slim armor, you just need to defeat the demonless, defeating her gives you your armor back plus grants you a dark spell.
I had a feeling about that I had managed to get her health down by 75+% on my second time fighting her I don't know how but for the most part I've just been figuring things out on my own hell last night on my first try I'd beat a mimic chest oh and speaking of mimic chests there is an item I got from a mystery box it's something electric elemental item if you know where it goes or what it does please tell me and if I have any other further questions please go easy on me I do suffer from permanent brain damage making explaining and talking t o other people
Understanding a lot of the events requires listening carefully to what the characters say. But this could be difficult even for someone who doesn't have brain damage. The fortuneteller may be a good help. I can say from experience that throughout this game I never faced any bad turning point other than a game over from health depletion. Many characters are cruel, but they always turn out to be nice on some level. The game makes Celica a glutton for abuse.
P.S.: If you need help defeating the demoness, go visit the hot springs. There is an intricate set of events there but eventually you can gain powerful magic which will make her a pushover in comparison.