Keyaru, who is exploited and sexually abused repeatedly by others due to being a healing magician, notices what lays beyond just his healing magic, and is convinced that a healing magician is the strongest class in the world. However, by the time he realizes his own potential, he is already deprived of everything. Thus, using his healing magic, enhanced by the magic enhancing properties of the Philosopher's Stone on the world itself, he goes back four years into the past, deciding to redo everything and get revenge on the ones who abused him.
A compilation of the entire web novel! Volume 9 is the light novel, however.