If you are working at RIKEN and wish to bring your spouse and children to Japan, the family members can apply for "Dependent" status.
Spousal Work Visas
Companies are only able to sponsor the visa for the worker that is under contract.
If your spouse would like to begin work after arriving in Japan and is on a Dependent visa, he or she can apply for a permit to engage in activity other than that permitted by the status of residence previously granted. This permit usually limits the working hours to 28 hours per week or less.
If your spouse locates work with a Japanese company before arriving in Japan, the visa arrangements will need to be handled by that company.
For more information, see http://www.mofa.go.jp/j_info/visit/visa/index.html.