Lenders loathe him, and Hiroyuki Yagi, Buddhist monk-in-training and president of consultancy Central Research Institute, Inc., loves this reputation.

Yagi, a former debt-collector, made enemies of his former employers when he disclosed loopholes and negotiation tactics for debtors in his best-selling book "Karita kane wa kaesuna! (Don't Return Money You Borrowed!)"

The book, cowritten with financial entrepreneur and fiction writer Masakazu Kaji, has even been denounced in some quarters as "utterly immoral" and "threatening the downfall of Japan."