diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/UnityPath.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/UnityPath.cs
index ff74aeedf..5e3d312c6 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/UnityPath.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/UnityPath.cs
@@ -343,8 +343,8 @@ namespace UniGLTF
         }
 
         public static UnityPath FromAsset(UnityEngine.Object asset)
-        {            
-            var assetPath = AssetDatabase.GetAssetPath(asset);            
+        {
+            var assetPath = AssetDatabase.GetAssetPath(asset);
             if (string.IsNullOrEmpty(assetPath))
             {
                 throw new System.ArgumentNullException();
diff --git a/Assets/VRM10/Editor/MigrationMenu.cs b/Assets/VRM10/Editor/MigrationMenu.cs
index 39c62b578..d62cb76d8 100644
--- a/Assets/VRM10/Editor/MigrationMenu.cs
+++ b/Assets/VRM10/Editor/MigrationMenu.cs
@@ -6,14 +6,18 @@ namespace UniVRM10
 {
     public static class MigrationMenu
     {
-        static string s_lastPath = Application.dataPath;
+        static VRMShaders.PathObject s_lastPath = VRMShaders.PathObject.UnityAssets;
 
         const string CONTEXT_MENU = "Assets/Migration: Vrm1";
 
         [MenuItem(CONTEXT_MENU, true)]
         static bool Enable()
         {
-            var path = UniGLTF.UnityPath.FromAsset(Selection.activeObject);
+            if (Selection.activeObject == null)
+            {
+                return false;
+            }
+            var path = VRMShaders.PathObject.FromAsset(Selection.activeObject);
             var isVrm = path.Extension.ToLower() == ".vrm";
             return isVrm;
         }
@@ -21,27 +25,30 @@ namespace UniVRM10
         [MenuItem(CONTEXT_MENU, false)]
         static void Exec()
         {
-            var path = UniGLTF.UnityPath.FromAsset(Selection.activeObject);
-            var isVrm = path.Extension.ToLower() == ".vrm";
+            var path = VRMShaders.PathObject.FromAsset(Selection.activeObject);
 
-            var vrm1Bytes = MigrationVrm.Migrate(File.ReadAllBytes(path.FullPath));
+            // migrate
+            var vrm1Bytes = MigrationVrm.Migrate(path.ReadAllBytes());
 
-            var dst = EditorUtility.SaveFilePanel(
-                "Save vrm1 file",
-                s_lastPath,
-                $"{path.FileNameWithoutExtension}_vrm1",
-                "vrm");
-            if (string.IsNullOrEmpty(dst))
+            if (!s_lastPath.TrySaveDialog("Save vrm1 file", $"{path.Stem}_vrm1", out VRMShaders.PathObject dst))
             {
                 return;
             }
-            s_lastPath = Path.GetDirectoryName(dst);
+            s_lastPath = dst.Parent;
 
             // write result
-            File.WriteAllBytes(dst, vrm1Bytes);
+            dst.WriteAllBytes(vrm1Bytes);
 
-            // immediately import for GUI update
-            UniGLTF.UnityPath.FromFullpath(dst).ImportAsset();
+            if (dst.IsUnderAsset)
+            {
+                // immediately import for GUI update
+                Debug.Log($"import: {dst}");
+                dst.ImportAsset();
+            }
+            else
+            {
+                Debug.Log($"write: {dst}");
+            }
         }
     }
 }
diff --git a/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs b/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs
new file mode 100644
index 000000000..aef30c3b1
--- /dev/null
+++ b/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs
@@ -0,0 +1,183 @@
+using System;
+using System.IO;
+using UnityEditor;
+using UnityEngine;
+
+namespace VRMShaders
+{
+    /// <summary>
+    /// UniGLTF.UnityPath (Assets の ひとつ上がルート) をすべてのパスが扱えるように拡張するのが趣旨。
+    /// readonly struct で Immutable であるという主張。
+    /// </summary>
+    public readonly struct PathObject
+    {
+        /// <summary>
+        /// * Delemeter は / を保証
+        /// * .. を解決済み
+        /// * フルパス
+        /// * 末尾に / を付けない
+        /// </summary>
+        public string FullPath { get; }
+
+        public string Extension => Path.GetExtension(FullPath);
+
+        public string Stem => Path.GetFileNameWithoutExtension(FullPath);
+
+        public PathObject Parent => FromFullPath(Path.GetDirectoryName(FullPath));
+
+        public bool IsUnderAsset => IsDescendantOf(UnityAssets);
+
+        /// <summary>
+        /// AssetDatabase の引き数になるパスを想定。
+        /// Assets のひとつ上を 基準とする相対パス。
+        /// Application.dataPath は Assets を得る。
+        /// </summary>
+        /// <returns></returns>
+        public string UnityPath
+        {
+            get
+            {
+                var root = UnityRoot;
+                if (!IsDescendantOf(UnityRoot))
+                {
+                    throw new ArgumentException($"{FullPath} is not under UnityPath");
+                }
+                return FullPath.Substring(root.FullPath.Length + 1);
+            }
+        }
+
+        static PathObject? _root;
+        public static PathObject UnityRoot
+        {
+            get
+            {
+                if (!_root.HasValue)
+                {
+                    _root = FromFullPath(Path.GetDirectoryName(Application.dataPath));
+                }
+                return _root.Value;
+            }
+        }
+
+        public static PathObject UnityAssets => UnityRoot.Child("Assets/");
+
+        PathObject(string src)
+        {
+            if (string.IsNullOrEmpty(src))
+            {
+                throw new ArgumentNullException();
+            }
+            src = Path.GetFullPath(src).Replace('\\', '/');
+            if (src.Length > 1 && src[src.Length - 1] == '/')
+            {
+                // drop last /
+                src = src.Substring(0, src.Length - 1);
+            }
+            if (src[0] == '/')
+            {
+                FullPath = src;
+            }
+            else
+            {
+                if (src.Length >= 3 && src[1] == ':' && src[2] == '/')
+                {
+                    FullPath = src;
+                }
+                else
+                {
+                    throw new ArgumentException($"{src} is not fullpath");
+                }
+            }
+        }
+
+        public override string ToString()
+        {
+            try
+            {
+                var unityPath = UnityPath;
+                return $"<unity:{unityPath}>";
+            }
+            catch (ArgumentException)
+            {
+                return $"<file:{FullPath}>";
+            }
+        }
+
+        /// <param name="src">start with "X:/" on Windows else "/"</param>
+        /// <returns></returns>
+        public static PathObject FromFullPath(string src)
+        {
+            return new PathObject(src);
+        }
+
+        /// <param name="src">AssetDatabase が使うパス</param>
+        /// <returns></returns>
+        public static PathObject FromUnityPath(string src)
+        {
+            return UnityRoot.Child(src);
+        }
+
+        public static PathObject FromAsset(UnityEngine.Object src)
+        {
+            if (src == null)
+            {
+                throw new ArgumentNullException();
+            }
+            var assetPath = AssetDatabase.GetAssetPath(src);
+            if (string.IsNullOrEmpty(assetPath))
+            {
+                throw new ArgumentException($"{src} is not asset");
+            }
+            return FromUnityPath(assetPath);
+        }
+
+        public PathObject Child(string child)
+        {
+            return FromFullPath(Path.Combine(FullPath, child));
+        }
+
+        public bool IsDescendantOf(PathObject ascendant)
+        {
+            if (!FullPath.StartsWith(ascendant.FullPath))
+            {
+                return false;
+            }
+            if (FullPath.Length <= ascendant.FullPath.Length || FullPath[ascendant.FullPath.Length] != '/')
+            {
+                return false;
+            }
+            return true;
+        }
+
+        public byte[] ReadAllBytes()
+        {
+            return File.ReadAllBytes(FullPath);
+        }
+
+        public void WriteAllBytes(byte[] data)
+        {
+            File.WriteAllBytes(FullPath, data);
+        }
+
+        public void ImportAsset()
+        {
+            AssetDatabase.ImportAsset(UnityPath);
+        }
+
+        public bool TrySaveDialog(string title, string name, out PathObject dst)
+        {
+            var path = EditorUtility.SaveFilePanel(
+                title,
+                FullPath,
+                name,
+                "vrm");
+            if (string.IsNullOrEmpty(path))
+            {
+                dst = default;
+                return false;
+            }
+            dst = PathObject.FromFullPath(path);
+            return true;
+        }
+    }
+}
diff --git a/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs.meta b/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs.meta
new file mode 100644
index 000000000..0c5fa088f
--- /dev/null
+++ b/Assets/VRMShaders/GLTF/IO/Editor/PathObject.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d16607c9cf9d05e46b5beec82002d4ef
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs b/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs
new file mode 100644
index 000000000..04028497f
--- /dev/null
+++ b/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs
@@ -0,0 +1,28 @@
+using System.Linq;
+using NUnit.Framework;
+using UnityEditor;
+using UnityEngine;
+
+namespace VRMShaders
+{
+    public sealed class PathObjectTests
+    {
+        [Test]
+        public void Test()
+        {
+            var dataPath = PathObject.FromFullPath(Application.dataPath);
+
+            Assert.AreEqual("Assets", dataPath.Stem);
+
+            // UnityRoot
+            Assert.True(dataPath.IsDescendantOf(PathObject.UnityRoot));
+            // UnityRoot/Assets
+            Assert.False(dataPath.IsDescendantOf(PathObject.UnityAssets));
+            Assert.AreEqual(dataPath, PathObject.UnityAssets);
+
+            Assert.AreEqual(PathObject.UnityRoot.Child("Assets"), PathObject.UnityAssets);
+            Assert.AreEqual(PathObject.UnityAssets.Parent, PathObject.UnityRoot);
+            Assert.AreEqual("Assets", PathObject.UnityAssets.UnityPath);
+        }
+    }
+}
diff --git a/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs.meta b/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs.meta
new file mode 100644
index 000000000..23b001bcf
--- /dev/null
+++ b/Assets/VRMShaders/GLTF/IO/Tests/PathObjectTests.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 45383f6fca5a57246b70f3919b582b7d
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/VRMShaders/VRM/IO/Runtime/VRM.meta b/Assets/VRMShaders/VRM/IO/Runtime/VRM.meta
deleted file mode 100644
index 6d0ee19da..000000000
--- a/Assets/VRMShaders/VRM/IO/Runtime/VRM.meta
+++ /dev/null
@@ -1,8 +0,0 @@
-fileFormatVersion: 2
-guid: eb31f565eeca6164694b06ccfe3bc251
-folderAsset: yes
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: