A scenario approach is often used to envision sustainable futures. Several important scenario design factors are identified in the literature, which include the demonstration of deliberation and the participation of stakeholders; however, specific methodologies of scenario design are yet to be established. Accordingly, in this study, we demonstrate a series of workshops involving ordinary citizens for energy visioning in Suita city, Japan, and propose a new citizen-participatory scenario design methodology based on the combination of scenario design and future design approaches. It is shown that the inclusion of future generations in deliberation is effective for creating future visions in a specific context and deriving policy implications. Specifically, by analyzing the deliberation process and the proposed scenarios, it was confirmed that the scenarios proposed by future generations were proactive in terms of paying the costs incurred to facilitate the realization of policies toward achieving a long-term vision. Furthermore, even though the proposals made by the future generations imposed additional burdens for current generations, post-workshop scenario assessment revealed that current generations are supportive of these scenarios. It is concluded that the proposed methodology is effective since it can overcome uncertainties, include holistic scopes, and consider a long-term time horizon.

Much attention has been paid internationally to the adoption of sustainable development goals to achieve sustainable outcomes. Although roadmapping is widely used by companies and other organizations to plan long-term strategies, relatively few studies have examined the development of roadmapping methods aiming at sustainability. To address this challenge, in this article, a backcasting-based method to design roadmaps that could be used to facilitate decision making and plan sustainable futures is proposed. By drawing on the concept of backcasting, the proposed roadmap design method consists of two phases: defining a sustainable vision, and describing the pathways that are required to realize that vision. In order to develop pathways that bridge the gap between the present and the vision, we develop a roadmap template called a “four-arrow model.” To demonstrate the proposed method, roadmaps are developed for Japanese manufacturing from the present to 2050 by organizing an expert workshop. As a result, two different roadmaps that connected sustainable visions and associated pathways are successfully developed. The number of ideas generated through the workshop indicates that the proposed method encouraged brainstorming and concept development. Future research will focus on making the roadmap design process more comprehensive by conducting industrial case studies.