The goal of this study is to maintain dialogue motivation between users through the mediation of a dialogue robot. Previous studies proposed artificial agents that present dialogue topics to facilitate relationship-building among individuals for a short period. However, sustaining dialogue motivation between users using such agents has not been investigated. This study proposes an algorithm for presenting topics about other people to sustain dialogue motivation between users for certain periods. Specifically, we designed a dialogue robot that discusses topics of common preference, emphasizing high information content between users. To validate our approach, we applied the proposed algorithm to a dialogue robot and conducted experiments involving university and graduate students belonging to the same community. The results confirmed that our proposed method prevented them from decreasing their engagement in dialogue even after one month of their interaction with the robot. Additionally, topics with high information content were more likely to be remembered by users. In other words, these findings indicate that when a robot introduces a topic with high information content, participants might perceive it as unusual. This perception prompts them to retain the topic with clarity; as a consequence, it might enhance the participants’ willingness to engage in dialogue with each other. Based on the findings of this research, using highly informative topics in dialogue can be an effective strategy for cultivating long-term relationships among individuals. This also insight emphasizes the potential role of robots in facilitating human relationship-building. Future studies need to examine the effectiveness of the proposed method with various communities.