Suiseiseki is the third Rozen Maiden doll and she and her twin are called “gardeners” because of their ability to communicate with plants. This ability is also extended to tending for a human’s “soul tree”, representing what a person is really like deep inside.
But most people know her for her habit of saying “desu” at the end of almost every sentence.
Beautiful cosplay! I’m always amazed at the details of the costumes of Rozen Maiden cosplayers. Really great work on this one!