Toggle vi_mode mode with caps_lock so that hjkl keys function as arrow keys and u/i as delete and backspace.

karabiner.json

{
  "global":
  {
    "check_for_updates_on_startup": true,
    "show_in_menu_bar": false,
    "show_profile_name_in_menu_bar": false
  },
  "profiles":
  [
    {
      "complex_modifications":
      {
        "parameters":
        {
          "basic.simultaneous_threshold_milliseconds": 50,
          "basic.to_delayed_action_delay_milliseconds": 500,
          "basic.to_if_alone_timeout_milliseconds": 500,
          "basic.to_if_held_down_threshold_milliseconds": 500,
          "mouse_motion_to_scroll.speed": 100
        },
        "rules":
        [
          {
            "description": "toggle vi_mode with caps_lock",
            "manipulators":
            [
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 0
                  }
                ],
                "from":
                {
                  "key_code": "caps_lock",
                  "modifiers":
                  {
                    "optional":
                    [
                      "any"
                    ]
                  }
                },
                "to":
                [
                  {
                    "set_variable":
                    {
                      "name": "vi_mode",
                      "value": 1
                    }
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "caps_lock",
                  "modifiers":
                  {
                    "optional":
                    [
                      "any"
                    ]
                  }
                },
                "to":
                [
                  {
                    "set_variable":
                    {
                      "name": "vi_mode",
                      "value": 0
                    }
                  }
                ],
                "type": "basic"
              }
            ]
          },
          {
            "description": "Modify HJKL",
            "manipulators":
            [
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "h",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "left_arrow"
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "l",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "right_arrow"
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "j",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "down_arrow"
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "k",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "up_arrow"
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "u",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "delete_or_backspace"
                  }
                ],
                "type": "basic"
              },
              {
                "conditions":
                [
                  {
                    "name": "vi_mode",
                    "type": "variable_if",
                    "value": 1
                  }
                ],
                "from":
                {
                  "key_code": "i",
                  "modifiers":
                  {
                    "optional":
                    [
                      "caps_lock",
                      "command",
                      "shift",
                      "control",
                      "option"
                    ]
                  }
                },
                "to":
                [
                  {
                    "key_code": "delete_forward"
                  }
                ],
                "type": "basic"
              }
            ]
          }
        ]
      },
      "devices":
      [
        {
          "disable_built_in_keyboard_if_exists": false,
          "fn_function_keys":
          [],
          "identifiers":
          {
            "is_keyboard": true,
            "is_pointing_device": false,
            "product_id": 63100000,
            "vendor_id": 1452
          },
          "ignore": false,
          "manipulate_caps_lock_led": false,
          "simple_modifications":
          [
            {
              "from":
              {
                "key_code": "down_arrow"
              },
              "to":
              {
                "key_code": "right_control"
              }
            },
            {
              "from":
              {
                "key_code": "left_arrow"
              },
              "to":
              {
                "key_code": "right_control"
              }
            },
            {
              "from":
              {
                "key_code": "right_arrow"
              },
              "to":
              {
                "key_code": "right_control"
              }
            },
            {
              "from":
              {
                "key_code": "up_arrow"
              },
              "to":
              {
                "key_code": "right_control"
              }
            }
          ]
        },
        {
          "disable_built_in_keyboard_if_exists": false,
          "fn_function_keys":
          [],
          "identifiers":
          {
            "is_keyboard": true,
            "is_pointing_device": false,
            "product_id": 631,
            "vendor_id": 1452
          },
          "ignore": false,
          "manipulate_caps_lock_led": true,
          "simple_modifications":
          []
        },
        {
          "disable_built_in_keyboard_if_exists": false,
          "fn_function_keys":
          [],
          "identifiers":
          {
            "is_keyboard": true,
            "is_pointing_device": false,
            "product_id": 615,
            "vendor_id": 76
          },
          "ignore": false,
          "manipulate_caps_lock_led": true,
          "simple_modifications":
          []
        },
        {
          "disable_built_in_keyboard_if_exists": false,
          "fn_function_keys":
          [],
          "identifiers":
          {
            "is_keyboard": true,
            "is_pointing_device": false,
            "product_id": 601,
            "vendor_id": 1452
          },
          "ignore": false,
          "manipulate_caps_lock_led": false,
          "simple_modifications":
          []
        }
      ],
      "fn_function_keys":
      [
        {
          "from":
          {
            "key_code": "f1"
          },
          "to":
          {
            "consumer_key_code": "display_brightness_decrement"
          }
        },
        {
          "from":
          {
            "key_code": "f2"
          },
          "to":
          {
            "consumer_key_code": "display_brightness_increment"
          }
        },
        {
          "from":
          {
            "key_code": "f3"
          },
          "to":
          {
            "key_code": "mission_control"
          }
        },
        {
          "from":
          {
            "key_code": "f4"
          },
          "to":
          {
            "key_code": "launchpad"
          }
        },
        {
          "from":
          {
            "key_code": "f5"
          },
          "to":
          {
            "key_code": "illumination_decrement"
          }
        },
        {
          "from":
          {
            "key_code": "f6"
          },
          "to":
          {
            "key_code": "illumination_increment"
          }
        },
        {
          "from":
          {
            "key_code": "f7"
          },
          "to":
          {
            "consumer_key_code": "rewind"
          }
        },
        {
          "from":
          {
            "key_code": "f8"
          },
          "to":
          {
            "consumer_key_code": "play_or_pause"
          }
        },
        {
          "from":
          {
            "key_code": "f9"
          },
          "to":
          {
            "consumer_key_code": "fastforward"
          }
        },
        {
          "from":
          {
            "key_code": "f10"
          },
          "to":
          {
            "consumer_key_code": "mute"
          }
        },
        {
          "from":
          {
            "key_code": "f11"
          },
          "to":
          {
            "consumer_key_code": "volume_decrement"
          }
        },
        {
          "from":
          {
            "key_code": "f12"
          },
          "to":
          {
            "consumer_key_code": "volume_increment"
          }
        }
      ],
      "name": "Default profile",
      "parameters":
      {
        "delay_milliseconds_before_open_device": 1000
      },
      "selected": true,
      "simple_modifications":
      [],
      "virtual_hid_keyboard":
      {
        "caps_lock_delay_milliseconds": 0,
        "country_code": 0,
        "keyboard_type": "ansi",
        "mouse_key_xy_scale": 100
      }
    }
  ]
}