i got a story line here it is:
you start out as a soldier in the sith army and move up in the ranks and your character sometimes while in the middle of an intense battle sends out surges of energy(the force)but later on the dark jedi's start noticing you and your pontential of becoming a great sith lord so they have a dark jedi put you as their apprentice and you eventually become a dark jedi.Now even later on in-game your a leader of a sith army and durimg your missions there are keys events that affect your characters thinking and perspective of life.For example maybe while on a planet the natives are very friendly to you and accept you and there you decide whether or not you destroy them or decide to destroy all records of being there so events like this affect your thinking and if you stay on DS you eventually conquer most planets and you are the lord of all sith.But if you decide LS then you see that the sith are the seed of all hatred and seeing that you where once there leader you now there strengths and weaknesses.so you come out of hiding from the sith with a army of jedi knights and masters and you have one jedi as an assasin to become dark and eliminate the sith lords once and for all.
so long story short: start out as soldier move up the ranks and eventually dark jedi. main events effect the way you think of lifeand that would determine your LS or DS points in tha char info screen. so dark side path you conquer all but then the army destroy all you have and LS path destroys the sith and during the process you learn more about the force and train others to use the force.
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so thats it at a simple stage but i've thought it up with alot more detail thats just the whole overview about it.