The head of Japan's largest advertising agency will step down in January after the suicide of one of the company's workers, which was ruled by the government to be "death by overwork" - known as "karoshi" in Japanese.

"It is extremely regrettable that we could not prevent overwork by a new recruit," Tadashi Ishii told reporters at a news conference.  "In order to take full responsibility, I would like to resign as president at a board meeting in January."

It was a year ago that 24-year old Matsuri Takahashi took her own life.  She was a bright and talented graduate of prestigious Tokyo University.  After eight months on the job, she was logging more than 100 overtime hours per month, and her supervisors ordered her to under-report her OT.  Getting only two hours sleep per night, she left a note for her mother that asked, "Why do things have to be so hard?" and Ms. Takahashi jumped to her death from her company dormitory on Christmas Day.

In September, labor regulators ruled that her suicide was caused by overwork.  Last month, government agents raided the company headquarters.

This came at a time when Prime Minister Shinzo Abe was working on ways to cut back on Japan's overwork problem.  Workers at one in four Japanese companies are at risk of dying from Karoshi, working 80 hours or more of overtime per month last year.  They are unwilling to ask for overtime pay or better working conditions because of a cultural debt many feel towards employers.  Others feel the only path for advancement is by putting in more unpaid hours than coworkers.  The Labor Ministry acknowledges 100 karoshi deaths per year, but the experts agree that this number is only the tip of the iceberg. 

This is Dentsu's second high-profile case of karoshi.  Another workers, also 24-years old, committed suicide at company headquarters in Tokyo in 1991. Because of that earlier case, Dentsu is under the microscope for Ms. Takahashi's death.

"There is definitely going to be an impact from this case," said economist and professor Naohiro Yashiro of Showa University.  "Dentsu is a very big company and if these practices can continue to happen there, it means that it's necessary to put (stronger) regulations in place."