Willpower, guts, or determination — the grit or mental strength to persevere through difficulties.
根性で最後まで走り切った。
He pushed through to the end with sheer determination.
根性があれば何とかなると言われても、準備も大事だ。
Even if people say 'where there's a will there's a way,' preparation is also important.
あの選手の根性は本物だ。
That athlete's grit is for real.
根性だけでは解決できない問題もある。
There are problems that can't be solved by willpower alone.
One's character or disposition; the basic nature or temperament of a person (often used in a critical sense).
あの子は根性が悪く、人の成功を喜ばない。
That kid has a mean streak and doesn't rejoice in others' success.
彼の根性は真面目で勤勉だ。
His nature is earnest and hardworking.
根性のある人は困難でも簡単に諦めない。
People with strong character don't give up easily in the face of hardship.