Complete data set.

Cooperative relationships between humans and agents are becoming more important for the social coexistence of anthropomorphic agents, including virtual agents and robots. One way to improve the relationship between humans and agents is for humans to empathize with agents. Empathy can increase human acceptance. In this study, we focus on the IKEA effect in creating agents and examine empathy through interpersonal relationships. We conducted a robot assembly task in which participants either cooperatively built the same robot or individually assembled their own. The results showed that the IKEA effect promoted empathy toward the agent regardless of the relationship between participants. However, participants did not show a significant change in empathy levels from before to after the task. These results suggest that regardless of the relationship between participants, the IKEA effect can promote empathy toward the agent.