The Ministry of Health, Labour and Welfare (MHLW) has released the COVID-19 Contact- Confirming Application (COCOA) to prevent the spread of COVID-19. However, it is currently underuti- lized and its effectiveness is questionable. Therefore, we propose the nudge system that promotes people's voluntary installation and aims to increase the utilization of COCOA. The proposed system motivates users to install COCOA by reframing the installation as the acquisition of tickets to experience three attractive events: (1) paint, (2) vote, and (3) fortune slip. In this paper, we propose the nudge system promoting the installation and assume scenarios for the use of the system, taking into account the appropriate environment for each event.
