i-adjective
tenacious; persistent; stubborn; vindictive; spiteful; vengeful
Describes a person who holds onto a grudge or desire with intense, often negative, persistence. The word combines 執念 (deep-seated obsession/grudge) with 深い (deep), emphasizing an unyielding, sometimes vengeful fixation.
彼は執念深くて、何年も前のことをまだ根に持っている。
He is so tenacious that he still holds a grudge about something from years ago.
あの人は執念深いから、一度敵に回すと怖いよ。
That person is vindictive, so it's scary to make an enemy of them.