Miasma Physician

The alchemist-physicians of the 'Green Pouch Guild,' the only 'Judges of Life and Death' in the wasteland capable of fighting magic energy mutations and alchemical toxins.
After the Great Collapse, poisonous miasma and mutated plagues became the greatest killers of survivors, rendering ordinary herbs completely ineffective. The physicians of the Green Pouch Guild, using alchemical knowledge from the Age of Radiance combined with mutated plants from the wasteland, developed special potions that could suppress mutations and neutralize toxins. They constantly wear gas masks to resist poisonous miasma and pathogens, carry alchemical backpacks filled with various reagents, and their injector staves contain liquids that can both save and kill: green purification potions can instantly neutralize miasma and suppress mutations, while potent toxins can instantly incapacitate the fiercest mutated creatures. They travel between various settlements, healing the sick and saving lives, and also recovering dangerous alchemical pollutants. Some call them angels who save the dying and injured, while others say they are madmen who toy with toxins, but in the wasteland, no one dares to offend a miasma physician carrying hundreds of deadly potions.

Below is a light novel that fits the background story. Those interested can take a look.