Kaifuku Jutsushi No Yarinaoshi Vol. 1 (Light Novel)

Keyaru is a top-tier healing magician with the title of “Healer Hero,” but due to his lack of fighting abilities, his party sees him as nothing more than a tool. After being exploited again and again, and having lost everything, he becomes convinced that healing magic is the strongest type of magic in the world and decides to redo the last four years by using his magic to travel back in time. With all of his painful memories of what happened to him intact, he begins a quest for revenge against those who exploited him in this dark fantasy light novel by Rui Tsukiyo.
In Vol. 1, Keyaru begins his quest for revenge by going after Flare, a strong mage who got him addicted to a drug that made him lose his sanity.
Notice: This light novel is written in Japanese.