A Western is a type of story set in the western half of the United States roughly between the Civil War and 1914. Westerns commonly tell the stories of cowboys, gunfighters, outlaws, lawmen, Native Americans, and other colorful characters. Tropes from a western can turn up in other genres, such as space-based science fiction due to the focus both put on pioneering.
A Daria fanfic with a Western setting is usually a reinvention.
True Grit, by Charles Portis (adapted into film by Henry Hathaway in 1969 and by the Coen Brothers in 2010) obviously has nothing to do with Daria, but it's a damn good novel with a Daria-esque protagonist, so give it a read!
Westerns in Daria Canon
The only episode that relates to a Western trope is "Speedtrapped." The area Daria and Quinn drive through is a desert, and many of the people they encounter, including Travis and the clientele of Mad Dawg's, wear western clothing. However, though much of the episode evokes Western sensibilities and the plot involves coming to the rescue of a damsel in distress (and her band), it is arguable whether the episode qualifies as a Western.
Westerns and Daria Fanfiction
As Daria was set in the late 20th century in an area commonly believed to be in the U.S. Northeast, there are unsurprisingly few Daria Westerns written. In such stories, it is common that the characters from Daria are placed into a Western situation, as opposed to the canon universe diverting to a Western scenario. Often an existing Western is used as the basis for a crossover, parody, or reinvention ("retrofic").
Examples of Daria Westerns
- "The Cynic, The Fashionista and The Jackass," by Doggieboy
- "Daria: 1830," by Decelaraptor
- "Once Upon a Time in Lawndale," by Disco316
- "Tales of the Missouri Cheyenne," by Decelaraptor