Try UIM
iBus makes SKK private dictionary reset, so I look for other IME. Then, I found uim-skk.
Installing UIM is easy.
After installed above packages, edit ~/.xprofile. In my environment, ~/.xinitrc doesn't work.
if type uim-xim &> /dev/null ; then uim-xim & fi export XMODIFIERS='@im=uim' export GTK_IM_MODULE='uim' export UIM_IM_ENGINE='skk' uim-toolbar-gtk & uim-toolbar-gtk-systray &
Reference site is Uim を使って日本語を入力 - ArchWiki. The commands uim-toolbar-gtk and uim-toolbar-gtk-systray are different versions per GUI modules. My desktop is GTK2 base, so using uim-toolbar-gtk and uim-toolbar-gtk-systray.