결초보은하다 · 결초보은의 마음으로
repaying a kindness even after death, eternal gratitude
Example
이 은혜는 결초보은의 마음으로 꼭 갚겠습니다.
I will repay this kindness without fail, even beyond the grave.
Word parts
결 tie+초 grass+보 repay+은 kindness
Literally 'tie grass to repay kindness' — a ghost tied grass to trip his benefactor's enemy.