My paper discusses an East Asian notion of climate and its significance for sustainability. A particular reference is the environmental philosophy of Tetsuro Watsuji (1889–1960), a Japanese philosopher who reflected upon the meaning of climate, or “ fudo” in the Sino-Japanese linguistic tradition. Watsuji sees fudo not merely as a collection of natural features—climatic, scenic, and topographical—of a given land, but also as the metaphor of subjectivity, or “who I am”. Furthermore, this self-discovery through fudo is never private but collective. By referring to a phenomenological notion of “ ek-sistere”, or “to be out among other ‘I’s”, Watsuji demonstrates the pervasiveness of a climatic phenomenon and the ensuing inter-personal joining of different individuals to shape a collective sustainable measure in response to the phenomenon. My paper lastly concretizes the significance of fudo and its inter-personal ethical basis for sustainability by dwelling upon cross-ventilation in Japanese vernacular residential architecture. Cross-ventilation emerges only through what Watsuji calls “selfless openness” between different rooms predicated upon the joining of different ‘I’s soaked in hotness and humidity. Watsuji’s fudo thus offers a lesson that without considering the collective humane characteristic of a natural climatic phenomenon, any sustainable act is flawed and inefficient.