This paper introduces Blob Manipulation, the interaction technique with fluidic soft matter. Most of the soft matters are substances between liquid and solid and possess viscoelasticity. We focus on this materiality and propose a novel interaction technique. A stirring rod is used as the input tool. When the system detects a user input such as touching, rubbing or tapping, the corresponding transformation will be executed. Six basic operations were designed to transform fluidic soft matter geometrically and topologically. Rheological user interface associated with metamorphose is expected to pioneer new possibilities for design, education and entertainment.