Constellation:

Character:

The fourth doll of the Rozen Maiden collection and Suiseiseki's twin, Souseiseki possesses a sharpness in her speech that is similar to Shinku's, attacks ruthlessly in combat, and does not tolerate sub-par actions. She is also quite stubborn and very devoted to her masters. Her appearance is not only the most masculine of the dolls, but her speech is also noted to be of the masculine form, using the first person pronoun "boku" instead of gender neutral pronouns like "jibun" or "watashi." 

Source from Wikipeida