Communication robots are now getting popular. In particular, partner robots, which can perform personal services, are in high demand. However, they can be prohibitively expensive. Therefore, we considered a multi-user robot with a virtual agent service which could satisfy user demands. But, several issues need to be solved in order to achieve this purpose. Firstly, there is no general service platform for such robots. Secondly, even if we use the multi-user robot by executing the virtual agent service, the physical shape, and other characteristics of the multi-user robot sometimes creates a strong impression on users. Therefore, we proposed a virtual agent service platform, and the robot features modification for a multi-user robot. The robot can autonomously adjust its position according to each user's physiological signals, which based on emotion in real-time. We presented a preliminary evaluation to determine whether the proposed method could improve users' robot experience even for the users who are not familiar with the robot at all.