Darkest Dungeon

Characters gain Quirks (positive and negative) through interacting with a dungeon object (like an altar, an idol, a stack of books, etc) or by gaining resolve levels. Each character can have 5 positive and 5 negative quirks at once, after which, a random quirk will disappear to acomodate a newly acquired quirk.

In town, one of the buildings you will unlock will be the Sanatarium. Here, you can cure diseases, remove negative quirks, and lock in positive quirks to make them permanent.

In order to remove a negative quirk, enter the sanitarium, select a hero, put them in the Treatment Ward (top row), then select a negative (red) quirk from the list and hit the check mark.

Once you have completed your weekly quest, the achievement will pop.