how to switch (back and forth) between hiragana-mode and direct-mode with shift key

[Un1Gfn]

~/.config/ibus-kkc/rules/default/keymap/hiragana.json

{
  ...
  "define" : {
    "keymap" : {
      ...
      "Tab" : "set-input-mode-direct",
      "Shift" : "set-input-mode-direct",
      ...
    }
  }
}

Tab works, but Shift does not work.