expression, noun
mortal enemy; sworn enemy; nemesis
A strong, literary set phrase for an irreconcilable enemy one cannot coexist with under the same sky. Often used in dramatic or historical contexts.
彼は私にとって不倶戴天の敵だ。
He is my mortal enemy.
あの一族とは不倶戴
We have a sworn-enemy relationship with that clan.