Lately, social and economic innovation, which is mostly implemented by businesses, is gaining significance. Particularly, the business of creating relationships and value simultaneously, which the author calls “relationship business,” has been strongly recommended for social innovation. To implement the relationship business, it is important to consider the business model design methodology, which includes the design process, business modeling, and analysis of its environment. Among them, the design process needs to be considered initially, given that the design is performed not by individuals but by a team. In this paper, we will discuss the design process of the relationship business by reviewing existing design processes, and propose a spiral-based design process, which consists of phases such as start-up, survey, ideation, prototyping, and research. (This work was supported by JSPS KAKENHI Grant Number JP19K01859.)