If you are using pbibtex in TexShop and have Japanese bib file encoded in sjis, then you need to specify the kanji code as sjis in order to properly format the Japanese bibtext entries. This can be done either by command line as
$ pbibtex projname -kanji=sjisor by the TexShop Preferences --> Engine dialog under default bibtex engine specification by setting
pbibtex -kanji=sjis