Souseiseki : lapis luzuli stern,lapis luzuli star
Voiced by: Rika Morinaga (Japanese), Julie Ann Taylor

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." Souseiseki's presence is much more significant in the anime than in the manga. These all being stereotypical traits of a tomboy.

In the manga, Souseiseki's master wanted to use her power to enter other people's dreams and exact revenge on his brother's lover, who he felt had stolen his brother from him. Since Souseiseki alone could not achieve this goal, she fights Suiseiseki to gather the two gardeners' tools, the shears (which is her primary weapon) and the watering can, which together can affect an individual's soul tree. She eventually realizes that it is her master's heart that needs to be freed and sacrifices herself to do so. The dolls present are shocked by Souseiseki's actions and Suigintou uses the confusion to snatch Souseiseki's Rosa Mystica, enraging both Shinku and Suiseseki. In the latest chapter, it is revealed that Souseiseki's body is currently manifested by Kirakishou.

In the anime, Souseiseki is devoted to a lonesome old man, who uses her as a substitute for his deceased son, Kadzuki. Souseiseki apparently does not have a medium, because Motoharu Shibasaki was never shown to have a rose ring. She is shown to be slightly more eager, probably from a sense of duty, to participate in the Alice Game than her sisters. In the OVA, she is introduced in the flashback in mid-fight with Shinku and later does not hold back in attacking a then-harmless Suigintou. Throughout Rozen Maiden Träumend, she questions her idyllic lifestyle, and, much to Suiseiseki's disappointment, takes part in the Alice Game out of devotion to Rozen after being accosted by Barasuishou, who was believed to be the seventh Rozen Maiden doll to fulfill his wish of finding Alice and relieve his perceived grief. She battles Suigintou, but is defeated and loses her Rosa Mystica.

Even though the two versions progress differently, Souseiseki is still the first doll to lose her Rosa Mystica, and her Rosa Mystica transfers to Suigintou on both occasions. However, at the end of Rozen Maiden träumend, Laplace is seen dancing with two Rosae Mysticae, one of which is believed to be Souseiseki's. To add to the confusion, after Shinku is resurrected by "Father," she tells Jun that Souseiseki's and Hinaichigo's losing their Rosa Mysticae is her burden to bear. The most likely reason for this is that essentially they were under the care of her medium, which makes sense for Hinaichigo, but not so much for Souseiseki.

In the manga, Souseiseki has gone missing from her case, after Suiseiseki tells Souseiseki's master that she found her sister's hat in the N-field. Later, in the last volume of the manga, she is reunited with Suiseiseki. Souseiseki tells Suiseiseki that she didn't want to play the Alice Game anymore, because she didn't "want to go against the Suiseiseki that I love". Soon afterwards she dies once again, growing rose vines and a white rose out of her right eye. Though she is the first doll to lose her Rosa Mystica, Souseiseki is actually the second doll to lose in the Alice Game. In the latest chapter of Rozen Maiden Tale, it is revealed that while Suigintou has her Rosa Mystica, Kirakishou has her body. And, because Jun from the alternate dimension has inadvertently kissed the ring, it may grant Souseiseki the revival Suiseiseki wished for. This however was hindered by the fact that Suigintou currently has Souseiseki's Rosa Mystica and she refuses to release it. So in the end, Suiseiseki gives Souseiseki her Rosa Mystica, allowing Souseiseki to return to life. To restore the worlds to their orders, Souseiseki convinces Suigintou to temporarily restore her Rosa Mystica while she returns Suiseiseki's. As soon as Suiseiseki is restored, they combine their powers to restore the world orders. Afterward, she readies to return her Rosa Mystica as promised, but Suigintou breaks the agreement. The Jun from the other parallel dimension decides to turn Souseiseki to his younger counterpart's Rozen Maiden, as they are the same person.

Her artificial spirit is named for a fragrance by Lolita Lempicka. Souseiseki was also the first runner-up for Saimoe 2005.

Medium: Motoharu Shibasaki (Anime) / Kazuha Yuibishi (Manga) / Jun Sakurada (alternate dimension, manga) / Jun Sakurada (Manga)
Artificial Spirit: Lempicka (レンピカ, Renpika^?)