I wonder if he'll end up altering history as he does these
There have been nothing to suggest that beating a past event changes it in any way.
But considering MC is a reincarnation its not impossible, just unlikely.
I find it more likely that MC can do things others cant because of what an anomaly he is.
That said, there has been a established fact that you can get objects from them.
So a wild counter theory, what if the "reward" for clearing this one is the "saveable party" itself ?
That would fuck up some people emotionally for sure xD