Damn, this started somewhat interesting showing the world, the dangers and then giving us a glimpse of why the MC is a "cheat".
Then went the flashback arc showing how she became so, and... Honesty, I kinda expected it sooner or later, but it went completelly different from expected. She was OP, so the expected flashback would be to show both how she acquired such power and give us a hint of what would be the threat in the future that would challenge even her. Yer...
Even ignoring the lack of noticeable hooks for future plot, it was at the same time too long and too rushed - as in, it took a while but the solution just seemed to come out of nowhere, all at once.
This ending kinda kills it. It was all because she was literaly chosen to... well, the plot of SMT Nocturne if there was only one person there. And she chose the Freedom Ending a.k.a. keep the world as it is. Only without the fighting in the middle