a competitive spirit; an unwillingness to lose; a disposition to keep trying and compete hard.
彼は負けん気が強く、試合で最後まで諦めない。
He has a strong competitive spirit and never gives up until the end of a match.
負けん気のおかげで、厳しい練習にも耐えられた。
Thanks to his competitive spirit, he could endure the tough training.
小さいころから負けん気で、何でもライバルと競ってきた。
Since childhood he has been competitive, always competing with rivals at everything.