do not break the laws of your faction, otherwise you will be punished, possibly executed. so no shinigami who go round killing other shinigami whenever they like.
you may not use another persons character or npc in your personal story or mission, unless they allow you to. doing so will reduce your grade to 0.
you may not kill/maim/permenantly injure/remove powers, another persons character, unless they allow you to, even in trainings.
the only exception to the previous rule is the battlefield. when two people go there, anything can happen to either character, and anything should. there will be no, i beat him, but i liked him, so i let him live, unless it is well within your characters personality. otherwise your grade will be 0. but you can make a good escape, if you think it through.