noun
willpower; guts; determination
Refers to mental toughness, perseverance, and the drive to overcome difficulties. Often used in contexts of sports, work, or personal challenges.
彼は根性があるから、どんな困難にも負けない。
He has guts, so he won't be defeated by any hardship.
根性を出して最後まで走り抜いた。
I showed determination and ran through to the end.
noun
character; nature; disposition
Describes a person's innate temperament or moral character. Less common than the willpower sense; often appears in fixed expressions like 根性が曲がっている (have a warped character).
あの人は根性が曲がっているから、信用できない。
That person has a warped character, so I can't trust them.
彼の根性の悪さには呆れる。
I'm disgusted by his mean nature.