Answer
The pen name Osamu Dazai was adopted by Shūji Tsushima, a prominent Japanese author of the 20th century. This pseudonym became synonymous with his literary works and is widely recognized in the literary world. Under the name Osamu Dazai, Tsushima explored various themes in his writings, including alienation, despair, and human suffering, capturing the attention and admiration of readers both during his lifetime and beyond.