The old man cursed the invaders as "eastern devils."
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Strong WWII-era slur for Japanese soldiers/people. Treat as historical/literary vocabulary — using it today is hostile and offensive. The neutral term is 日本人.
history
东洋 ("Eastern Ocean") was the period name for Japan; 鬼 means "devil." The compound spread during the 1931-1945 anti-Japanese resistance and parallels 洋鬼子 used for Westerners.