http://myanimelist.net/forum/?topicid=584169
http://www.mediafactory.co.jp/bunkoj/20130411/index.html
Apparently he died of cancer.
Don't have much else to say, other than he left a couple of ZnT chapters unfinished, and he also did a number of other stories.
http://en.wikipedia.org/wiki/Noboru_Yamaguchi_(author)
Edit: I cannot into words apparently.
I saw that today. It's a damned shame, especially cancer. Rest in peace.
Terrible. At only 41 years old too. Cancer research can't happen fast enough.