Sister Denmark is a minor character--oddly enough, since as a Danish woman she is the most obvious choice to stand in for Humon herself. Most of the sisters are very similar to their male counterparts, but Sister Denmark exemplifies the trend by having a tomboyish appearance such that she can be mistaken for a man. The details of her appearance vary as Humon searches for the right equilibrium between recognizable (to the readers) femaleness and in-universe masculinity. One noticeable difference between her and Brother Denmark is that she is often depicted smoking.
Sister Denmark and Sister Norway have the same ambiguous best friends/possible lovers relationship as Denmark and Norway. The two Denmarks once got into an argument over which Norway has better boobs. She seems to be jealous of Sister Sweden and sometimes annoyed by her, but the two are still more compatible as friends than their brothers, especially when watching porn together.