firefly (jepella rebellion) (honkai: star rail)
An official alternate costume worn by Firefly during the events of the Jepella Rebellion.
Unlike her fellow Stellaron Hunters, her outfit isn't shown during Myriad Celestia Trailer: The Jepella Rebellion — Scene 47, due to not appearing as herself at any point during the video (she instead appears as SAM); her outfit during the rebellion is seen during a flashback CG during the Penacony story arc.
While her skirt is canonically a long black skirt, some fan artists depict it as a pencil skirt under the assumption that she is the female figure standing above Kafka in her splash art (Danbooru post #7689897).