I don't have any personal postdoc grant now. But, you can get a postdoc position through JSPS (Japan Society for the Promotion of Science). This is a popular way to get a postdoc position in Japan, since most universities in Japan do not have their own postdoc positions. See https://www.jsps.go.jp/english/e-inv/application/ for the application guideline. Please contact me if you're interested in.