Fuji no Yamai wa Fushi no Yamai.

A catastrophic event has thrust the world into an age where disease begets disease. Ostracized for his unconventional treatment methods, the dark Doctor Ikuru is stricken with an immortalizing disease. On a desperate mission to die, he must save a world desperate to live. This medical science-fiction adventure will go to the very edge of humanity and back in one man's search for an ending to his suffering, all while saving the world he wishes to leave.

Note: The manga got originally published as a short series of 4 chapters on February, 2020 in Shounen Jump +. On September 6, 2022, the manga got serialized and its 4 original chapters got republished as part of the serialization.