diff --git a/Legacy/Legacy.csproj b/Legacy/Legacy.csproj
index dbd44a4c..31bdec36 100644
--- a/Legacy/Legacy.csproj
+++ b/Legacy/Legacy.csproj
@@ -101,6 +101,7 @@
     <Compile Include="System21\ImageBET.cs" />
     <Compile Include="SystemAqua\ArcDAT.cs" />
     <Compile Include="Tsd\ArcMCD.cs" />
+    <Compile Include="Unknown\ArcDAT.cs" />
     <Compile Include="Uran\ArcNCL.cs" />
     <Compile Include="Uran\ArcPHS.cs" />
     <Compile Include="Weapon\ArcDAT.cs" />
diff --git a/Legacy/Unknown/ArcDAT.cs b/Legacy/Unknown/ArcDAT.cs
new file mode 100644
index 00000000..2ac912b8
--- /dev/null
+++ b/Legacy/Unknown/ArcDAT.cs
@@ -0,0 +1,102 @@
+//! \file       ArcDAT.cs
+//! \date       2018 Jan 23
+//! \brief      'Unknown' resource archive.
+//
+// Copyright (C) 2018 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.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using System.Linq;
+using GameRes.Utility;
+
+// [010629][Unknown] No Reality
+
+namespace GameRes.Formats.Unknown
+{
+    [Export(typeof(ArchiveFormat))]
+    public class DatOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DAT/UNKNOWN"; } }
+        public override string Description { get { return "'Unknown' resource archive"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return false; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            int count = file.View.ReadInt32 (0);
+            int entry_size = file.View.ReadInt32 (4);
+            int data_offset = file.View.ReadInt32 (8);
+            int index_size = count * entry_size;
+            if (!IsSaneCount (count) || entry_size == 0 || entry_size > 0x10
+                || index_size + 12 != data_offset)
+                return null;
+            var index = file.View.ReadBytes (12, (uint)index_size);
+            Decrypt (index);
+            var base_name = Path.GetFileNameWithoutExtension (file.Name);
+            int index_offset = 0;
+            var dir = new List<Entry> (count);
+            for (int i = 0; i < count; ++i)
+            {
+                int id = index.ToInt32 (index_offset);
+                var entry = new Entry {
+                    Name   = string.Format ("{0}#{1:D4}", base_name, id),
+                    Size   = index.ToUInt32 (index_offset+4),
+                    Offset = index.ToUInt32 (index_offset+8),
+                };
+                if (entry.Offset < data_offset || !entry.CheckPlacement (file.MaxOffset))
+                    return null;
+                dir.Add (entry);
+                index_offset += entry_size;
+            }
+            DetectFileTypes (file, dir);
+            return new ArcFile (file, this, dir);
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            var data = arc.File.View.ReadBytes (entry.Offset, entry.Size);
+            Decrypt (data);
+            return new BinMemoryStream (data, entry.Name);
+        }
+
+        internal void DetectFileTypes (ArcView file, IEnumerable<Entry> dir)
+        {
+            var buffer = new byte[4];
+            foreach (var entry in dir.Where (e => e.Size > 4))
+            {
+                file.View.Read (entry.Offset, buffer, 0, 4);
+                Decrypt (buffer);
+                uint signature = buffer.ToUInt32 (0);
+                var res = AutoEntry.DetectFileType (signature);
+                entry.ChangeType (res);
+            }
+        }
+
+        internal void Decrypt (byte[] data)
+        {
+            for (int i = 0; i < data.Length; ++i)
+                data[i] = Binary.RotByteR (data[i], 4);
+        }
+    }
+}