執念しゅうねん (shuunen)

彼かれの 勝負しょうぶにかける 執念しゅうねんはすごい

He is obsessed with the competition.

わしが執念深い男じゃなくて運がいいぞ。

and lucky for you as I'm not a revengeful man.

彼らは敵の執念深さに気づいていなかった。

They were unaware of the implacability of their enemy.

こうして、僧の執念は消え去ったのであった。

And the abbot's obsession disappears.

慈円は忠実を、「執フカキ（執念深い）人」と評している。

Jien describes how Tadazane was 'a vindictive person.'

画霊（がれい）は、人物画に画家の執念が乗り移ったとされる付喪神。

Garei (literally, the ghost of a picture) are said to be tsukumogami (spirits that inhabit certain objects) where a portrait has been possessed by the spirit of its painter.

罰･･･特質において、本来執念深い−M.R.コーエン punishments...essentially vindictive in their nature- M.R.Cohenあいつは執念深いから気をつけた方がいいよ。

Watch out for him. That guy can really hold a grudge.

この事業が完成できたのはひとえに彼の執念のおかげだ. It is his tenacity of purpose more than anything else that contributed to the completion of this project.その言葉を聞いて彼女の執念のすさまじさを垣間見る思いがした. Her words gave me a glimpse of her tremendous tenacity of purpose.同様に手紙の執念が妖怪化したものが文車妖妃ともいう。

As seen from the above, the spirit of letter that has become a specter is also called "Fuguruma-yobi."