Remembrance of former births', is one of the higher powers. I believe the writer has attained some of this higher knowledge, in order to write this story. As a matter of fact, where one makes a vow deeply in past lives and will try to fulfill it in future lives.
However, one does not recall everything in the past lives, it will be bit and pieces like a jigsaw puzzle. It takes time to piece everything together. Except for the last episode: where you need to forget the past lives in order for others to be safe, is not true.
I give it 8.5/10 marks. I sincerely wish that the writer can achieve more transcendent knowledge to write the next story. Keep up the good writing.