ibus-skk is an implementation of the SKK (Simple Kana-Kanji) input method on the IBus input method framework. Note that SKK works quite differently from other Japanese input methods. To learn about SKK, see:
If you build from the source, you will need to separately install libskk.
After installing it, do:
$ ./configure
$ make
$ sudo make install
GPLv2+
Copyright (C) 2011-2017 Daiki Ueno <ueno@gnu.org>
Copyright (C) 2011-2017 Red Hat, Inc.
This file is free software; as a special exception the author gives
unlimited permission to copy and/or distribute it, with or without
modifications, as long as this notice is preserved.
This file is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY, to the extent permitted by law; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.