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persistence; fortitude; indomitability
不屈の精神で困難を乗り越えてきた。
I have overcome difficulties with an indomitable spirit.
彼女の不屈な意志に皆が感銘を受けた。
Everyone was impressed by her indomitable will.
不屈の闘志で最後まで戦い続けた。
He continued fighting to the end with indomitable spirit.