One is wearing a shrine maiden outfit while the other is wearing a yukata. From what little I know of the Japanese, they're probably near a shrine on new years. Gudako is working as a shrine maiden and Mashu, being the good servant/buddy/partner/bunt of the joke she is, visited the shrine to give her master her support. And after reading a lot of the info 4-komas, seeing a Gudako act normal feels so... Weird.