Converters

The Converters panel (formerly "MMD Options") is the home for tools that convert models from one rig/format to another, plus MMD-specific cleanup. It's where you prepare a freshly imported model for Unity/VRChat.

It contains three areas:

1. Rigify conversion - convert a Rigify/Metarig armature to a Cats-compatible one
2. Platform conversion - Source/Valve and VRM fixes
3. MMD Cleanup - Fix MMD Model and rigid-body/joint removal

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Rigify → Cats

The Convert Rigify to Cats button is always visible, but is greyed out until a Rigify or Metarig armature is active. When Cats detects one, an info box appears and the button becomes available.

Fix MMD Model can't process a Rigify rig directly, so convert it first, then continue your normal workflow.

Options:

• Merge Twist Bones - fold Rigify's twist bones into their parents during conversion.

How to use:

1. Select your Rigify/Metarig armature.
2. When the button lights up, click Convert Rigify to Cats.
3. Continue with the rest of your workflow.

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Platform Conversion

Convert to Valve / Source Format

Prepares a model's armature for the Source engine (Source Filmmaker, GMod, etc.):

• Renames bones to the ValveBiped convention
• Adjusts the hierarchy for Source

When to use: exporting to Source Engine / Valve games.

Fix VRM Shapes

Repairs shape-key issues that commonly appear on VRM imports:

• Fixes VRM shape-key references
• Ensures VRM blendshapes map correctly

When to use: right after importing a .vrm, if its shape keys don't behave.

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MMD Cleanup

Fix MMD Model

This is the main tool for converting a fresh MMD/VRM model into a Unity/VRChat-ready rig.

⚠ WARNING: Fix MMD Model is only for fresh MMD / VRM imports that have NOT been set up for Unity.

DO NOT use it if:

• Your model was purchased from Booth, Gumroad or a similar store
• Your model has already been set up for Unity/VRChat
• You are building your own custom model from scratch

Fix Model was never a "fix anything" button. it's a converter for specific import formats. The same warning is shown in Quick Access, where the button also lives.

🚫 Ignore these warnings at your own risk. If you run Fix MMD Model on anything other than a fresh MMD/VRM import, after all the warnings Cats and this wiki give you, that is entirely on you. Do not open an issue about it you will be pointed straight back to these warnings and it will be closed immediately.

💡 The ⚙ settings gear next to the button opens Model Settings (keep end bones, keep twist bones, join meshes, connect bones, remove zero-weight, protected bones, etc.). See Settings for details.

What it does

1. Reparents bones - reorganizes the hierarchy for Unity
2. Removes unnecessary bones - strips MMD-specific/unused bones
3. Renames & translates - Japanese → English, standardized names (Translation)
4. Merges weight paints - redistributes vertex weights
5. Rotates hips - corrects hip rotation for Unity
6. Removes constraints - clears MMD-specific constraints/IK
7. Deletes unused vertex groups - cleans empty weight groups
8. Converts morphs to shape keys

How to use

1. Import your fresh MMD or VRM model via Quick Access.
2. Select the armature.
3. Click Fix MMD Model (in Converters or Quick Access).
4. Wait for it to finish (complex models can take a minute).
5. Review the result.

Remove Rigid Bodies and Joints

Removes MMD physics components (rigid bodies + joint constraints). VRChat uses Unity's physics, so MMD physics aren't compatible and should be removed.

How to use: select your model and click Remove Rigid Bodies and Joints.

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Typical MMD → VRChat Workflow

1. Import your .pmx/.pmd/.vrm via Quick Access.
2. Fix MMD Model (Converters or Quick Access).
3. Remove Rigid Bodies and Joints.
4. Combine Materials and other cleanup (Optimization).
5. Optimize - atlas, bone merging, remove doubles.
6. Set up Eye Tracking and Visemes.
7. Export an FBX for Unity via Quick Access, and set up materials in Unity.

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Common Issues

Model looks broken after Fix MMD Model it was probably already Unity-ready. Undo (Ctrl+Z), re-import the original, and don't run Fix MMD Model on it.

Bones have odd/English names this is expected; names are translated and standardized for VRChat.

Some materials are black usually fine; set materials up in Unity. You can also try Convert All to PNG in Optimization.

Model looks rotated in Blender Blender and Unity use different coordinate systems; export handles this and it'll be correct in Unity.

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VRM Notes

VRM models generally need the same treatment as MMD models:

• Run Fix MMD Model on fresh VRM files (VRoid exports, etc.)
• Run Fix VRM Shapes if the blendshapes misbehave
• Don't run Fix MMD Model on already-processed VRM models

Cats works alongside the VRM Add-on for Blender use it to import .vrm, then use Cats to process and optimize.

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Related Pages:

• Quick Access - Import/Export, and the other Fix MMD Model button
• Optimization - Post-conversion optimization
• Translation - Name translation
• Visemes / Eye Tracking - Avatar feature setup

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Last Updated: July 28, 2026 | Plugin Version: 5.2.3.0 | Blender: 5.1 & 5.2 (5.2 LTS recommended)