Constantly mistaken for a boy, Souseiseki is Suiseiseki's twin sister. She possesses a sharpness in her speech, attacks ruthlessly in combat, and does not tolerate sub-par actions. Her appearance is not only the most masculine of the dolls, but her speech is also noted to be of the masculine form, since using the first person pronoun "boku" instead of gender neutral pronouns like "jibun" or "watashi.
She is shown to be slightly more eager, probably from a sense of duty, to participate in the Alice Game than her sisters. She questions her idyllic lifestyle, and much to Suiseiseki's disappointment, takes part in the Alice Game out of devotion to Rozen, to fulfill his wish of finding Alice and relieve his perceived grief.Souseiseki's weapon is The Gardener's Scissors which complements her sister's and her artificial spirit, Lempicka (pronounced "Renpika") is named for a fragrance by Lolita Lempicka.