The third Rozen Maiden doll, and Souseiseki's older twin. She and Souseiseki are both referred to as "gardeners" for their ability to communicate and tend not only to regular plants, but also to the "soul trees" of humans.
In the anime, Suiseiseki's first impression is different than that of the manga. She appears very shy and nervous, and is very distrustful of humans because one had kidnapped Souseiseki. Shinku once described Suiseiseki as being the most shy and timid of the Rozen Maidens.
Rozen Maiden Papercraft - Suiseiseki