bitter enemy
父の仇敵を討つために武芸を磨き続けた。
He kept honing his martial arts to take revenge on his father's bitter enemy.
長年の仇敵同士がついに和解を果たした。
Long-standing bitter enemies finally achieved reconciliation.
仇敵と知りながらも命を救う決断をした。
He decided to save a life despite knowing it was his bitter enemy.