Not a legal professional but I'll try to add some context.
In Japan, it is hard to dismiss a worker.
Supreme Court decision on Kouchi Housou case (1977) might provide context.
A radio announcer over slept two times in two weeks, resulting in missing a 10 minute 6AM news segment, once completely, the second time partially.
The radio station dismissed (fired) the announcer.
The Supreme Court ruled that the dismissal was invalid, because dismissal of the worker was too harsh and would not receive general social approval.
I'm not going to go into the detailed reasoning behind the decision but, put simply, dismissal of a worker is only allowed as a last resort. Even if the company is in financial difficulty or the employee has made a huge mistake that resulted in losses to the company, unless the company can prove that firing that worker was the last resort: that despite the companies best effort to provide education/training good work environment etc, that dismissing the worker was necessary (i.e. socially deemed acceptable), the dismissal might be ruled invalid.
Basically the employers are expected to educate and nurture their worker. Unless a worker is explicitly hired for a specific skill, the worker is expected to conform to company needs and the company is expected to train and educate the worker so they can perform the needed task. So when the company hits hard times or if an employee's skill sets becomes unwanted, the company is expected to reassign you within the company even if the said work is unrelated to the employee's skill set.
However, if such reassignments are done with the intent of coercing them to quit "of their own will," it's abuse of employer authority and is illegal. There are many cases of such lawsuits and I believe there is a lawsuit pending involving a current Konami employee who previously worked as a game designer. An update in 2014 indicated that Konami assigned him to be a play tester along side part-time workers. As far as I know, Sony has also been implicated in such illegal abuse as well. Some times these things happen because of personal reasons, sometimes it happens because of financial reasons.
At the end of the day, companies and workplaces involve people interacting with each other. And there's always both sides to the story. ALWAYS.
If the alleged reassignments happened with the intent to have people quit, sue the company, it's illegal in Japan.
I really can't find Japanese dismissal law issues written in English except for this one
http://www.mfj.gr.jp/web/lunch_seminar/documents/2008-01_Kanbayashi_doc.pdf