KOKORO is the title of a famous novel written by Soseki Natsume in 1914. It is said to be the most sold book in Japan. Soseki Natsume is most famously printed on the 1000 yen bill that circulated in 1984. His version of the bill was removed from circulation in 2007.

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https://www.amazon.com/Kokoro-Natsume-Soseki/dp/0895267152