/usr/share/linuxdoc-tools/mappings/nippon/mapping is in linuxdoc-tools 0.9.72-4build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/linuxdoc-tools/mappings/nippon/../groff/tr-mapping
/usr/share/linuxdoc-tools/mappings/nippon/../groff/tr-mapping