Obviously, these humans are different from humans in real life. It'll be interesting to see the ways in which they differ and are the same.
Yeah, living for 1000 years can give you a different outlook on life in general and how you treat others. I'll try my best to portray that notion in the story.
I question why this is a thing. It just seems so illogical to me.
Perhaps that's one of the downsides of living for a long time. Your moral sense grows dull and you become desensitized to the point where you lose your respect for humanity. This is especially true to the ones in power. Authority figures get a power trip on controlling people (you see this even in RL). If there is a reason why slaves have to fight for their freedom, its because the society of ZIN is fixated on labels and social status. To them, slaves should remain slaves and citizens should remain citizens. If a slave were to break the order of things, society gets bitter. Not only that, but its a reaction to the public's fear. Keep in mind, the plantations are there to keep the planets healthy. If 45-50% of the slaves were to become dead batteries on one of the three planets, it would spell doom for not only the humans living on that planet, but all life living on it. That fear lives with the citizens on a daily basis (to top it off, they live on average for 1000 years). So its no wonder they don't look at slaves as proper human beings, but tools to keep them alive. If a tool breaks, its deemed useless.
Kinda sounds like this is happening just for the sake for throwing more conflict at your characters, but I'm guessing there are more important reasons behind this.
Well, its not just about revenge. Their intentions are derived from fear that the angels will try to repeat what they did to them thousands of years ago. And yes, the USZ has ulterior motives aside from fear and revenge.
I don't know what your work ethic is like (or anything about you for that matter), but 11 characters sounds like too much to work with. I imagine it would be difficult to create unique enough personalities, fighting styles, backstories, and roles in the plot to justify having all of them.
I base the personalities on the anime hair system. Certain hair colors represent the characters' personality. For example: Black hair might represent independence, purple hair egotistical, orange courageous, red passionate, green jealousy, etc. With that said you'll see some similarities personality wise, but that's on purpose. In fact, you may notice that two completely different characters will say the same phrase or two. As for backstories and roles in plot, I have confidence in my creativity. I see a number of possibilities these characters can have in regards to their social links and experiences. I'll add more fighting styles to make sure that all 11 characters are unique (either that, or make 2-3 common fighting styles). Oh, I almost forgot to mention this. Just because there are 11 playable characters doesn't mean you'll meet all 11 characters during your playthrough. In Mortal realm 1, some characters can only be acquired if you choose a certain job. For example, if you choose demon hunter, you'll get Eclaire and Alex. Others will join later by default no matter what job you choose.