From the publisher's website:
Modern-Day Exploration of the Land of the Rising Sun
Japan is a contradictory nation of ancient traditions and modern high-tech free enterprise. Within its dark shadows and hidden places, Great Old Ones, Outer Gods, and their monstrous servitors lie in wait for the unwary. In the corporate boardrooms and political offices, secret societies carry out their sinister agendas. In hoary shrines and temples, Shinto kami and Buddhist bodhisattvas provide ancient knowledge and alien enlightenment to those who remember the old ways. Cutting-edge corporate laboratories uncover forbidden secrets and create new horrors born of human science and the corrupting power of the Mythos. The mass media bombards the population with escapist entertainment and crass materialism while the madness of cosmic truth slowly seeps through, burrowing into the popular consciousness.
Welcome to the Land of the Rising Sun, where you will discover that the horrors of the Cthulhu Mythos are not limited to the West.
SECRETS OF JAPAN provides detailed information for playing CALL OF CTHULHU adventures in a modern Japanese setting. This book includes new character occupations, new spells, new monsters, new organizations, and rules for playing Japanese investigators. Also included are three adventure scenarios, two short stories, a glossary of cultural terms, details on Shinto and Buddhism in a CALL OF CTHULHU setting, extensive cultural background notes, and the secret history of Japan!