The back cover blurb pretty much says all that you need to know:  "For the first time in English, Osamu Dazai's hilariously comic (!) and deeply moving prequel to No Longer Human."

... but we'll throw these in for good measure:

"What I despise about Dazai is that he exposes precisely those things in myself that I most want to hide." – Yukio Mishima

"Dazai was an aristocratic tramp, a self-described delinquent, yet he wrote with the forbearance of a fasting scribe," – Patti Smith

Perhaps closer to a novella than a novel. 

Opening line: "Welcome to Sadness. Population one."