We propose an alternative approach called the Possessed Robot method to find each robot's unique communication strategies. In this approach, the human manipulator behaves as if she/he possesses the robot and finds the optimal communication strategies based on each robot's shape and modalities. We implement the Possessed Robot system (PoRoS) including a reconfigurable body robot, an easier manipulation system, and a recording system to evaluate the validity of our method. We evaluate a block-assembling task by PoRoS by turning on and off the modality of the robot's head. Subsequently, the robot's motion during player's motion significantly increases whereas the ratio of confirmatory behaviour significantly decreases in the head-fixed design. Based on the results, we find an example case for the optimal communication strategy in the head-fixed design. In this case, the robot leads the users and the user follows the robot as in the turn-taking communication style of the humanlike condition. This result shows the feasibility of the Possessed Robot method to make appropriate strategy adjustments based on the robot design.