This paper examines a Business Model (BM) from a socio-economic system perspective to discern key factors and understand its interactions resulting in the Scaling of Social Impact (SSI) in Social Entrepreneurship (SE). Previously, studies have explained the importance of the BM in relation to SE. However, there is a lack of empirical studies on how a BM’s transitions through participation of various actors result in the SSI, causing a gap in this field’s research. This research applies a qualitative analysis on a single case study of a Japanese social startup, “mymizu”, the first water refill application platform in Japan. The findings show that collaboration amongst different stakeholders on the initial phase of the BM could increase awareness of responsible consumption, convert into actual users for sustainability, and change their behavior. Secondly, members of society could take on dual roles, both as users and collaborators in the BM, which results in an exponential scaling effect of the Social Impact (SI). This paper contributes towards adding a Participatory Stakeholder (PS) to the ecosystem of the SSI and building a Regenerative BM (RBM) that is relevant in SE towards sustainability.