When the suicide of a female worker at ad giant Dentsu Inc. was recognized as karoshi, or death from overwork, many blamed a corporate culture that glorifies the "warrior" workers who sacrifice themselves for the good of the firm.

But the true problem behind the suicide at 24 of Matsuri Takahashi, who had clocked more than 100 hours of overtime in October 2015 before jumping from a corporate dorm on Christmas, is legal loopholes that allow employees to effectively work unlimited hours, according to an expert.

Takahashi's mother, Yukimi, is demanding that the government abolish those loopholes and create a better overall working environment.