This chapter explores the philosophical significance of breath and air within the Japanese martial art of aikidō (合氣道) through the lens of phenomenology, in particular transformative phenomenology. By examining this practice and making explicit the structural dimensions of breathing within it, the article considers the philosophical framework of aikidō for thinking air, breath, and atmosphere as relational, unsubstantial forces that shape bodily interaction. Focusing on the phenomenon of ki (気/氣) and the practice of aiki (合氣), aikidō is approached as a somatic and transformative discipline, in which breathing—far from merely being part of a physiological process—takes on the primary function of cultivating and coordinating energetic, bodily, and atmospheric relations in practice and motion. Drawing not only on the classical instructions of aikidō’s founder and the current teachings of contemporary aikidō masters but also on personal longstanding practice, the chapter investigates aikidō as a bodily field and philosophical methodology grounded in dynamic perception and radical relationality. After a brief introduction to the purpose and scope of this chapter, I will outline the historical intentions of its founder—Ueshiba Morihei (植芝盛平, 1883–1969)—for aikidō as both a bodily and spiritual practice. After this, I will discuss ki (気/氣) and aiki (合氣) as constitutive phenomena closely linked to breath and air that undermine the rigid distinctions between body and mind, subject and object, inside and outside, and individual and universal. Then, I will turn to the “radical relationality” within the practice space of aikidō, examining the unsubstantial, dynamic, and conflictual nature of the complex interplay observed between practitioners. Following discussion of the key principles and techniques aimed at reorganizing relational dynamics, particular attention will be devoted to kokyū (呼吸) techniques—especially kokyū hō (呼吸法) and kokyū nage (呼吸投げ)—in which breathing constitutes the very form and efficacy of these techniques.