Track whether you spend 183 days in South Korea during the current calendar year. South Korean tax residency may also arise from maintaining an abode in Korea for a continuous period of at least 183 days spanning two tax years; use the separate “183 Continuous Days” rule to track that case. Other factors, including domicile, family and employment, may establish tax residency independently of the day count.
https://www.law.go.kr/법령/소득세법