坚强成性
[jiān qiáng chéng xìng]
The netizen names themselves as 'Toughness as a nature'. It means this person regards being tough and firm as a kind of personal trait that they are endowed with from birth, or what has been formed in life after lots of practice and cultivation. They have built a very tenacious and strong-willed character, never give up easily in face of adversity and always strive against it.