Swarm User Interfaces allow dynamic arrangement of user environments through the use of multiple mobile robots, but their operational range is typically confined to a single plane due to constraints imposed by their two-wheel propulsion systems. We present corobos, a proof-of-concept design that enables these robots to cooperatively transition between table (horizontal) and wall (vertical) surfaces seamlessly, without human intervention. Each robot is equipped with a uniquely designed slope structure that facilitates smooth rotation when another robot pushes it toward a target surface. Notably, this design relies solely on passive mechanical elements, eliminating the need for additional active electrical components. We investigated the design parameters of this structure and evaluated its transition success rate through experiments. Furthermore, we demonstrate various application examples to showcase the potential of corobos in enhancing user environments.