For a long time,
A large part of North Korea was occupied by China.
BC 109—BC 108,
The Western Han Dynasty destroyed Korea,
There are four counties in this area: Le Lang County, Xuantu County, Fan Zhen County and Lintun County.
It is also known as the "Han Four Counties". During the Wei and Jin Dynasties, the central government still maintained its advantage over the Korean Peninsula.
The influence of Han culture on the Korean peninsula is far-reaching.
So Chinese characters are normal in Korea.