diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index d814fa64..3e154001 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -256,6 +256,7 @@
     <Compile Include="ArcASAR.cs" />
     <Compile Include="Artemis\ArcMJA.cs" />
     <Compile Include="Leaf\LeafVideo.cs" />
+    <Compile Include="LightVN\ArcMCDAT.cs" />
     <Compile Include="Macintosh\ImagePICT.cs" />
     <Compile Include="Macromedia\ArcDXR.cs" />
     <Compile Include="Macromedia\AudioSND.cs" />
diff --git a/ArcFormats/LightVN/ArcMCDAT.cs b/ArcFormats/LightVN/ArcMCDAT.cs
new file mode 100644
index 00000000..e4b1330f
--- /dev/null
+++ b/ArcFormats/LightVN/ArcMCDAT.cs
@@ -0,0 +1,193 @@
+//! \file       ArcMCDAT.cs
+//! \date       2026-5-27
+//! \brief      LightVN Engine mcdat resource archive
+//
+// Copyright (C) 2026 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using System.Linq;
+using System.Text;
+using Newtonsoft.Json;
+
+namespace GameRes.Formats.LightVN
+{
+    internal class McdatArchive : ArcFile
+    {
+        private readonly Dictionary<string, string> mMap;
+        private readonly string mRoot;
+        private readonly byte[] mKey;
+
+        public McdatArchive(ArcView arc, ArchiveFormat impl, ICollection<Entry> dir, 
+                            Dictionary<string, string> map, string root, byte[] key)
+                : base(arc, impl, dir)
+        {
+            this.mMap = map;
+            this.mRoot = root;
+            this.mKey = key;
+        }
+
+        public string GetFilePath(string name)
+        {
+            if (this.mMap.TryGetValue(name, out string relativePath))
+            {
+                return Path.Combine(this.mRoot, relativePath);
+            }
+            else
+            {
+                return string.Empty;
+            }
+        }
+
+        public void RestoreSize()
+        {
+            foreach(Entry e in this.Dir)
+            {
+                string path = this.GetFilePath(e.Name);
+                if(!string.IsNullOrEmpty(path) && System.IO.File.Exists(path))
+                {
+                    FileInfo fi = new FileInfo(path);
+                    e.Size = (uint)fi.Length;
+                }
+            }
+        }
+
+        public void Decrypt(byte[] data)
+        {
+            McdatArchive.Decrypt(data, this.mKey, 100);
+        }
+
+        public static void Decrypt(byte[] data, byte[] key, int length)
+        {
+            int dataLen = data.Length;
+
+            int decLen;
+            if (length < 0)
+            {
+                decLen = dataLen;
+            }
+            else
+            {
+                decLen = Math.Min(dataLen, length);
+            }
+
+            for (int i = 1; i < decLen; ++i)
+            {
+                byte k = key[i % key.Length];
+                data[dataLen - i] ^= k;
+            }
+
+            for (int i = 0; i < decLen; ++i)
+            {
+                byte k = key[i % key.Length];
+                data[i] ^= k;
+            }
+        }
+    }
+
+    [Export(typeof(ArchiveFormat))]
+    public class McdatOpener : ArchiveFormat
+    {
+        public override string Tag => "MCDAT/LightVN";
+        public override string Description => "LightVN Engine resource archive";
+        public override uint Signature => 0u;
+        public override bool IsHierarchic => true;
+        public override bool CanWrite => false;
+
+        public McdatOpener()
+        {
+            Extensions = new string[] { "mcdat" };
+        }
+
+        private static readonly string smIndexRelativePath = "\\Data\\_\\0.mcdat";
+        private static readonly byte[] smDefaultKey = new byte[]
+        {
+            0x64, 0x36, 0x63, 0x35, 0x66, 0x4B, 0x49, 0x33, 0x47, 0x67, 0x42, 0x57, 0x70, 0x5A, 0x46, 0x33,
+            0x54, 0x7A, 0x36, 0x69, 0x61, 0x33, 0x6B, 0x46, 0x30,
+        };
+
+
+        public override ArcFile TryOpen(ArcView file)
+        {
+            if (!file.Name.EndsWith(smIndexRelativePath))
+            {
+                return null;
+            }
+
+            string root = file.Name.Remove(file.Name.Length - smIndexRelativePath.Length);
+            byte[] key = this.QueryKey();
+
+            byte[] index = file.View.ReadBytes(0L, (uint)file.MaxOffset);
+            McdatArchive.Decrypt(index, key, -1);
+
+            Dictionary<string, string> map = null;
+            try
+            {
+                string json = Encoding.UTF8.GetString(index);
+                map = JsonConvert.DeserializeObject<Dictionary<string, string>>(json);
+            }
+            catch
+            {
+                return null;
+            }
+
+            if (map == null)
+            {
+                return null;
+            }
+
+            List<Entry> entries = new List<Entry>(map.Count);
+            foreach (string name in map.Keys)
+            {
+                Entry entry = Create<Entry>(name);
+                entry.Offset = 0L;
+                entry.Size = 0u;
+                entries.Add(entry);
+            }
+
+            McdatArchive mcdatArc = new McdatArchive(file, this, entries, map, root, key);
+            mcdatArc.RestoreSize();
+            return mcdatArc;
+        }
+
+        public override Stream OpenEntry(ArcFile arc, Entry entry)
+        {
+            McdatArchive mcdatArc = (McdatArchive)arc;
+
+            string path = mcdatArc.GetFilePath(entry.Name);
+            if (!string.IsNullOrEmpty(path) && File.Exists(path))
+            {
+                byte[] data = File.ReadAllBytes(path);
+                mcdatArc.Decrypt(data);
+                return new MemoryStream(data, false);
+            }
+            return Stream.Null;
+        }
+
+        private byte[] QueryKey()
+        {
+            return smDefaultKey;
+        }
+    }
+}