AbstractIn 2017, David Henry Hwang reworked his Tony Award‐winning play M. Butterfly (1988). This paper explores how Hwang wrote and rewrote M. Butterfly from the perspective of ethical literary criticism, probing into the role of brain text played in the process of drama writing. By investigating the variations of the Madame Butterfly story—from love legend to spy story—and the Madame Butterfly image—from Madame Butterfly to M. Butterfly, from Oriental Butterfly to Chinese Butterfly—this paper explains the forming of Hwang's brain text and his creation of M. Butterfly, the decoding of brain text and his writing of two Monsieur Butterflies, as well as the recoding of brain text and his building of a new cultural identity. It argues that brain text determines the playwright's writings and styles, and the dynamic revisions of M. Butterfly can be the manifestation and reconstruction of Hwang's brain texts, which represent his ethical choices made in the process of writing and rewriting. The metamorphosis of “Butterfly” in the two scripts of M. Butterfly reveals the playwright's dynamic thoughts on culture, gender, and identity: cultural stereotypes and the power relation between East and West; the cultural misunderstanding of Orientalism; and gender identity and fluidity in the twenty‐first century.