Isshun de Chiryou Shiteita no ni Yakutatazu to Tsuihou Sareta Tensai Chiyushi, Yami Healer Toshite Tanoshiku Ikiru

Life hasn't been kind to Zenos. He was born in the slums, and his dirt-poor background has denied him almost every opportunity. After an encounter with a healer, he throws himself into studying to become one and finally catches a break when an adventurer invites Zenos into his party. Zenos is thrilled—so thrilled, in fact, that he's willing to put up with his teammates treating him like garbage. They fail to appreciate his talents and ultimately kick him to the curb, claiming he's outlived his usefulness to them. Now bereft of money and out of options, Zenos decides to put his self-taught skills to use elsewhere and opens an underground clinic. Word quickly spreads about the brilliant healer working incredible magic in the city's shadowy underbelly. Even the royal palace is taking notice... Can Zenos buck the odds and carve out a life for himself in a world that's done nothing but spit in his face? And can he save the lives of the patients who wind up on his doorstep in the process? (Source: J-Novel Club)