Matsutake mushrooms harvested in Japan can cost over $500 per kilogram. Mushroom foragers like Gihei Fujiwara search for matsutake once a year around early fall. But it's hard to predict the quality of a harvest. Over the past 70 years, Japan's harvest has declined by over 95%. Now the mushrooms future is unclear. So what makes these mushrooms so expensive? And why have they almost disappeared?