The Institute for the International Education of Students (IES) Tokyo Center hosts students from colleges in the United States each semester. This exploratory research examines whether or not Japanese host families experience 'intercultural development' and create a sustainable new culture called a 'new space' through hosting the IES students. Questionnaires were sent to a total of 51 current and past host families in order to see their behavioral and cognitive shifts such as communication style, language usage, expression of interest in Japanese culture, individualism/collectivism, egalitarianism/hierarchy, and cultural relativism. The research finds that some characteristics displayed by the host families during the homestay are an informal communication style, increased English usage, and higher interest in Japanese culture. Nonetheless, increased English usage and higher interest in Japanese culture are unique only during the homestay although the informal communication style shows sustainability even after the homestay. Thus, the sustainable 'new space' created is more informal, and the 'intercultural development' found in this research is a shift in communication style. In order for the host families to recognize these cognitive changes, it is necessary to provide opportunities for training in intercultural development and cultural value differences.