From the site:
"In this project, we will develop a robot capable of rough terrain locomotion by its rolling and jumping. A robot consisting of deformable soft body and flexible actuators can roll and jump on a ground by the deformation of its deformable body."
Im too lazy to read their papers, but I would guess they are using SMA's . . .http://www.ritsumei.ac.jp/se/~hirai/research/softrobot-e.html
(videos and publications can be found at the bottom of their webpage)
The robot is also capable of climbing hills and even jumping!
No Japanese robot is complete without an anime looking lady to demonstrate it