Minimal Karabiner-Elements rules for moving focus to the next/previous window in the JIS keyboard layout.

command_at_to_backtick.json

{
    "description": "Change ⌘@/⌘⇧@ to ⌘`/⌘⇧`, respectively.",
    "manipulators": [
        {
            "from": {
                "key_code": "open_bracket",
                "modifiers": {
                    "mandatory": ["command"],
                    "optional": ["any"]
                }
            },
            "to": [
                {
                    "key_code": "grave_accent_and_tilde",
                    "modifiers": ["command"]
                }
            ],
            "type": "basic"
        },
        {
            "from": {
                "key_code": "open_bracket",
                "modifiers": {
                    "mandatory": ["command", "shift"],
                    "optional": ["any"]
                }
            },
            "to": [
                {
                    "key_code": "grave_accent_and_tilde",
                    "modifiers": ["command", "shift"]
                }
            ],
            "type": "basic"
        }
    ]
}