I Have Too Many Regrets

This book is also called "The hosts I have possessed are all so miserable" and "I will take you all to rewrite your life and reach the peak of glory" This is the story of an Earth high school student who became an immortal old monster after his death. In order to make up for the various regrets he had while alive, he kept reincarnating and rewriting various tragic life stories. Oh, by the way, how did this so-called immortal old monster die? One day, on a whim, I wrote a prescription for a thousand-year-old magic, followed it, and died.