Fujii Kōji, considered the pioneer of modern Japanese housing, was the first Japanese architect to design houses based on a scientific study of climate. Conducted in the 1920s, his study is closely related to matters of taste and is part of a dual process: the pursuit of a Japanese dwelling suited to the Japanese climate and cultural tastes. Understanding Fujii Kōji's place in this process, especially when compared to the first Japanese housing theorist, Yasuoka Katsuya, sheds light on the significance of climate in the development of modern Japanese housing. This paper explores the role of climate and the environment in the emergence of eclectic Western Japanese housing, the rise of Western-style housing, and Yasuoka's quest for an ideal housing suitable for modern Japan. This analysis highlights Fujii's innovative thinking and reveals its unique characteristics. While his architectural philosophy shares many similarities with Yasuoka's, his scientific approach to climate as the foundation for architectural design was truly innovative.