Use citoid to add ncid and naid as separate fields, as these IDs are frequently used when referring to Japanese research. (Similar to how we use PubMed, an NIH identifier used in US research). The method is to call CiNii API which returns these fields.
Some useful links as follows.
Specifications of NDL API: http://iss.ndl.go.jp/information/wp-content/uploads/2017/11/ndlsearch_api_all_20170329_en.pdf
Specifications of CiNii API: https://support.nii.ac.jp/en/cia/api/a_json
Zotero translator for CiNii: https://github.com/zotero/translators/blob/master/CiNii.js