Konami code is the unique code consisted of combination of keys used in Metal Gear games to give you specific surprises in the game (Up, Up, Down, Down, Left, Right, Left, Right, B, A).
As you probably know, there is no way to enter it via the keyboard. Despite this fact, you can enter Konami code without having physical controller using one simple trick, emulating the controller.

In Metal Gear Rising: Revengeance, Konami code unlocks:
1. Boss fights only under Chapter Select;
2. Revengeance difficulty ( ordinary way to unlock it is to beat the base story or Jetstream Sam DLC story on Hard and then Very Hard difficulty).

First of all, you will need a working phone and a PC connected to the same Wi-Fi network as the phone.
You will also need the DroidJoy app installed on your mobile device and DroidJoy server installed on your PC, so you can emulate the Xbox controller on youc PC using your phone.
You can download both from this link[grill2010.github.io].

As I mentioned earlier, first make sure your phone and PC are connected to the same Wi-Fi network.
Next, follow these steps:
1. Open DroidJoy Server on your PC and confirm when it asks you to install the neccessary controller driver.
2. Open DroidJoy on your phone, then tap the "Connect" button.
3. Your phone will automatically register your PC if connected to the same network, so just confirm the device.
4. Next, tap the "Gamepad" button on the app.
5. Choose the Jump 'n' Run template.
6. After doing so, open Metal Gear Rising: Revengeance on your PC.
7. Enter the combination of keys via the phone (Up, Up, Down, Down, Left, Right, Left, Right, B, A).
8. After successfully entering the combination, you will hear Raiden saying "Metal Gear Rising Revengeance", which means your code has been registered.

After successfully entering the code, you will have access to the Revengeance mode and ability to play boss battles only from the chapter select without the need for replaying whole chapters.
Also, you can do the same trick with any emulator for any controller.
I hope this guide has been helpful :)