I use this book, an autobioraphical work, paired with Year of Impossible Goodbyes.  It does not matter which book you start with, having the counter-point book is vital for the other side of what people are going through during this time period.

The Koreans living through Japanese occupation and then Korean/Communist rule, the sufferings of the Koreans comes through.  The Japanese who have been living in Korea and not part of the ruling powers and at risk when the Japanese move out and the Korean/Communists take over.

Both of these books are more than credible and essential to the understanding of the culture of two of the worlds continuing leaders of the world.

This book definitely focuses on what, in the larger picture, is not the central issue vis-a-vis Korean-Japanese relations during World War II. The use of sex slaves by the Japanese Army is still a major issue today. While it's true that some Japanese suffered during the war while in Korea, the vast majority of suffering took place on the Korean side.

That does not mean that this is not a valuable and interesting book. Anyone teaching this subject that uses this book should also probably introduce a book about the atrocities committed by the Japanese Army.

Is it credible? Sure. If you use it as what it is, it is credible: it is a fictionalized account of one person's experiences of the horrors of war. If you treat it that way—as fiction (not fact), and as a retelling of what one person saw-- yes, it is credible.

Now, if you're asking if this text should be taught as a history of the war, or if it gives a complete account of Japanese-Korean relations, the answers are no, and no-- but then it does not claim to do so. Therefore, using it by itself as a textbook for studying this period would not be appropriate. Instead, you might try placing it in context with other accounts of the war, and discussing how historians determine truth, accuracy, and what weight to give differing accounts.

Greg