The MH21-S R&D consortium (MH21-S) established in 2019 advances technological development toward the commercialization of Japan’s offshore methane hydrate resources. This research is conducted as a part of MH21-S, funded by the Ministry of Economy, Trade, and Industry. Under the global trend toward decarbonization, there is a strong demand to combine methane hydrate production with CCS (carbon dioxide capture & storage) technology. Among the various possible combinations, we need to define the target architecture and develop strategic plans for it. However, the uncertainty and complexity of the socio-technical system make it challenging to derive a consensual decision. In this paper, we propose a co-creative approach engaging various stakeholders through workshops and model-based discussion. The workshop was designed to gather ideas from stakeholders from various backgrounds. The ideas raised in the workshops were analyzed to construct a morphological matrix to generate a comprehensive solution space. A simulation model was developed to quantitatively evaluate the wide variety of concepts, by integrating several element models, such as economic evaluations models, gas production models, and production system models. The model interface was designed to support the understanding of the complex system. Through the demonstration of this approach, we have developed a model that can provide quantified evaluations of concepts that support the consensual decision-making of the target architecture.