Based on the video tutorial by Derek Pascarella (ATeam) (https://www.youtube.com/watch?v=ycVAZJv6TYE), here is a manual for setting up and using Virtual Per-Game VMUs with OpenMenu on the Sega Dreamcast.

Manual: Virtual Per-Game VMUs on Dreamcast (OpenMenu)

1. Introduction

This feature allows you to have a dedicated virtual VMU for every single game you play, effectively giving you unlimited save space. It works by backing up your physical VMU's content to an SD card connected via the serial port and restoring it when you load a specific game.

2. Requirements

Sega Dreamcast console.
OpenMenu (Version 1.5 or higher).
GDEMU (or similar ODE).
Original/OEM VMU (Visual Memory Unit).
Serial SD Card Adapter (Inexpensive adapters, often ~$15).
SD Card formatted to FAT32 (Older/smaller capacity cards often work better).

3. Initial Setup

Insert Hardware: Plug your Serial SD Adapter (with SD card) into the serial port on the back of the Dreamcast. Insert your original VMU into your controller.
Verify Detection: Boot into OpenMenu. If your SD card is recognized, you will see a "Serial VMU" option in the Settings menu.
Enable Feature:

Go to Settings.
Toggle Serial VMU to ON.
Target VMU: Choose the Port and Socket where your physical VMU is inserted (Default: Port A, Socket 1).
VMU Multi-Slot: Set to OFF for now (starts with 1 slot per game).

Save Settings:

Go to the Save/Load menu.
Select the Serial SD Card to save your OpenMenu settings. Note: You cannot save settings to the physical VMU while Serial VMU is active.

4. How to Use

Starting a Game (First Time)

Launch a game from OpenMenu.
You will see a prompt: "No existing serial VMU was found."
Choose "Format VMU" to wipe the physical VMU and create a fresh, dedicated "virtual" card for this game.

Warning: This deletes everything on the physical VMU currently inserted. Ensure you have backed up any important saves first.

The system will format the VMU (a small icon appears on the VMU screen).
The game will launch with a completely empty VMU ready for saves.

Saving and Playing

In-Game: Save your game as you normally would to the VMU.
Returning to Menu: When you quit the game and return to OpenMenu (e.g., via In-Game Reset), the system automatically backs up the current physical VMU data to the Serial SD card.
Relaunching: Next time you launch that specific game, OpenMenu automatically restores that game's specific VMU data from the SD card to your physical VMU.

Transferring Existing Saves (Importing)

If you have saves on another VMU that you want to move into a virtual slot:

Highlight the game in OpenMenu.
Press the button for "Exit to BIOS".
Select "Create or Restore Serial VMU + Exit to BIOS".
Once in the BIOS File Manager, remove the current VMU (which now holds the "Virtual" data) or insert a second VMU into another slot.
Copy the save file from your source VMU to the VMU configured for the game.
Return to OpenMenu. The system will detect changes and back them up to the Serial SD card.

5. Advanced Features

Multi-Slot Support (Up to 5 Slots per Game)

Enable: Go to Settings and toggle VMU Multi-Slot to ON.
Usage: When you launch a game, a menu appears letting you choose Slot 1 through Slot 5.
Use Case: Great for games with limited save slots or for keeping DLC separate (e.g., Sonic Adventure DLCs).

PC Management & Hidden Features

You can manage your saves by plugging the Serial SD card into a computer.

Folder Location: /openmenu/saves/[Game_ID]/
Identify Games: Open title.txt in the game folder to see the readable game name.
Export/Import:
Use a tool like VMU Explorer to open the .vmu files.
You can export individual saves (.vmi/.vms) or import downloaded saves into the virtual VMU file.
Custom Slot Names (Hidden Feature):
Create a text file in the game folder named slot2.txt (or corresponding slot number).
Write a custom name inside (e.g., "DLC Pack 1").
This custom name will appear under the slot selection menu in OpenMenu.

Troubleshooting Tips

SD Card Recognition: If the adapter isn't seen, try a different (older/slower) SD card.
Hot Swapping: If you accidentally remove the targeted VMU, OpenMenu will prompt you to select a new target from available VMUs.