Well to start off with, the "sister" can't use spirit magic, what that thing can do is steal powers temporarily from others, notice i'm saying that thing, her "sister" is actually a demon who possessed her dead sister's body (she died at birth along with the mother, mother made a pact with a demon for revenge, demon used it for it's own plans), there is a prophecy that the master of the water spirit that her family holds will be born in this generation and would save the world, and must be protected at all costs, the MC is basically required for the world in some way, can't remember what (possibly as some form of barrier) but after she was executed, all hell broke loose, literally, demons ran rampant etc, basically the gates of hell opened up shortly afterwards, as for how does this involve the father?
Either the father is the one who brought her back to life, her brother, or the son of the viscountess, the problem is the brother is young when this happens still, while some refer to the users eyes being the sign it was the viscountess's son (he has blue eyes)as well as him working in the magic field, other signs point to the father being the one to reverse time hence why his reasons for reversing it are heavily up to your interpretation, he could have done it for selfish reasons such as trying to save his own ass, or it could have been regret, if it's regret it puts his actions in a different light, if it's not him or he did it to save his own ass, then it makes him even worse, hence probably why the author left so much about the one who reversed time up in the air, to give people a chance to make different interpretations.
