Neurasthenia became a common disease and caused widespread concern in Japan at the turn of the twentieth century, whereas only a couple of decades earlier the term “nerve” had been unfamiliar, if not unknown, to many Japanese. By exploring the theories and practices of breathing exercise—one of the most popular treatments for neurasthenia at the time—this paper attempts to understand how people who practiced breathing exercises for their nervous ills perceived, conceived, and accordingly cared for their nerves. It argues that they understood “nerve” based on their existing conceptions of qi. Neurasthenia was for them a disorder of qi, although the qi had assumed modern appearances as blood and nervous current. The paper hopes to contribute to the understanding of how the concept of nerves has been accepted and assimilated in East Asia. It also points out the need to understand the varied cultures of nerves not only at the level of concept and metaphor, but also at the level of perception and experience.