The fourth Rozen Maiden doll, and Suiseiseki's tomboyish twin sister. As with Suiseiseki, she is a gardener that has the power to enter human dreams, and carries a set of pruning shears that she uses to tend humans' soul trees. She wields these in battle combined with acrobatic flight, her spirit Lempika and her hat which can be thrown and returns like a boomerang, a tactic she used to temporarily disarm Shinku in their second fight. She also has heterochromatic eyes like Suiseiseki, but the colors are the mirror image of her sister's. Her personality is also the polar opposite of Suiseiseki; she is rational, calm, quiet and deeply devoted to her master and to her duties, including the Alice Game. She possesses a sharpness in her speech that is similar to Shinku's, 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, 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.

In the manga, her master wanted to use Souseiseki's 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 of the Gardener and the watering can of the Gardener, 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.

The dolls present are shocked by Souseiseki's actions and Suigintou uses the confusion to snatch Souseiseki's Rosa Mystica.
In the anime, Souseiseki is devoted to a lonesome old man, who uses her as a substitute for his deceased son, Kazuki. 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, 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 to Suigintou in both instances. 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 Mystica's is her burden to bear. The most likely reson for this is that essentially they were under the care of her medium, which makes sense for Hinaichigo but only to an extent with Souseiseki. Though she is the first doll to lose her Rosa Mystica, Souseiseki is actually the second doll to lose in the Alice Game.
Recently in the manga, Souseiseki's body was missing from her case. It was found out that Kirakishou used Souseiseki's body to be able to set foot on the human world. Kirakishou tried to stop Shinku, Suigintou and Suiseiseki from retrieving back Souseiseki's body by forcing older Jun to be her medium and permanently having that body. Though Jun accidentally made a contract on Suiseiseki's ring, which was sooner found out that it was Souseiseki's ring, Kirakishou started leaving her body. The only step needed to bring Souseiseki back is to get her rosa mystica from Suigintou.

Due to Suigintou's stuborness, she didn't give it back resulting Suiseiseki putting her own rosa mystica in her twin. They soon meet Souseiseki, revieved, with Suiseiseki, lifeless. Suigintou was telling Shinku that the Souseiseki they are seeing is a trap of the 7th doll, which the truth is not. According to Souseiseki, Rozen used to say that among seven rosa mysticas, the only two allocated to Suiseiseki and Souseiseki were different from others, by chance they were mutually paired in the begining and they were also called twin stones. Therefore, Suiseiseki took a chance on putting her rosa mystica into Souseiseki's body as substitution with knowledge of a risk of failure.

Suigintou described that Souseiseki's approach as unbeautiful. Souseiseki not just agreed with her but also thought that she needs to get the rosa mystica back to where it should be. Still, she intended not to do that then and there but to prioritized escaping from Kirakishou's field with Shinku and Suigintou.

Soon they all meet with older Jun and Kanaria, with Souseiseki introducing herself to her medium (since he made a contract with her). The group then saw a big imitation clock. Shinku and the others were discussing how to restart it. Souseiseki noticed the clock had been made of wood at that time and then she said she may well be able to make it re-activated if she gains the cooperation of Suiseiseki because they are capable of controlling plant lives.

To restart the clock, Souseiseki needed to resurrect Suiseiseki. And thus, Souseiseki tried borrowing her Rosa Mystica from Suigintou only during rebooting the clock by a deal that Souseiseki will really accept Suigintou as a winner and remove the pain lingering on Suigintou's body instead of borrowing the Rosa Mystica.

Suigintou first looked apparently unreluctant, she eventually seemed to approve the deal. In this way, Suiseiseki came back to life. Souseiseki, however, determined to tell Suiseiseki a lie for the first and last time before resurrecting her. So, about how Suiseiseki could be back in, Souseiseki just explained it to her as follows; "Suigintou returned the Rosa Mystica." And then Suiseiseki ironically spoke to Suigintou, "I think better of you than I did before."

Suiseiseki also asked Souseiseki, "Can we be together for eternity after returning to the original world?" and Souseiseki replied to her "Yes." This is her first and last lie because Souseiseki promised to give her Rosa Mystica back to Suigintou after restarting the clock.
After restarting the wooden clock, two branches were reveled. as this is the connection of the wound world and the not wound world. Then they saw how Shinku collapsed and broke into pieces for time has run out. While the older Jun was crying over what is happening to Shinku, Suigintou immediately demanded Souseiseki to do the deal. Suiseiseki was confused and was about to go after Suigintou but Souseiseki stops her and tells her the deal. Suigintou stopped Suiseiseki from interfering while Souseiseki was about to give her rosa mystica to Suigintou. But just in time, younger Jun and Kanaria returned to them with Shinku's real body. They explain what happened to the body and how Hina Ichigo's rosa mystica guarded the body. Suigintou was surprised in what Hina Ichigo did in spite that their destiny is the Alice Game. Suigintou told Souseiseki not to continue with the deal because this made her think. Though she told Souseiseki not to be mistaken because Souseiseki's body is just for storage, and her rosa mystica is still Suigintou's property. Suigintou flew away while Suiseiseki was relieved and overjoyed being with her twin sister again. Older Jun told Souseiseki that her ring will go to the younger Jun in their world since both of them are still 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: Shibasaki Motoharu (Anime) / Yuibishi Kazuha (Manga)/Jun Sakurada (alternate dimension, manga)/ Jun Sakurada (real one. This is because the alternate Jun transfered the ring to the younger Jun because Souseiseki can't stay in the not wound world. Manga.)

Artificial Spirit: Lempicka