diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index bc3b18c8..095fc216 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -142,6 +142,7 @@
     <Compile Include="Cadath\ImageCGF.cs" />
     <Compile Include="Carriere\ArcARC.cs" />
     <Compile Include="Carriere\ImageCGD.cs" />
+    <Compile Include="CatSystem\ArcDAT.cs" />
     <Compile Include="CDPA\ArcPACK.cs" />
     <Compile Include="Cmvs\ArcCPZ1.cs" />
     <Compile Include="Cmvs\CpzHeader.cs" />
@@ -314,7 +315,9 @@
     <Compile Include="Software House Parsley\ArcUCG.cs" />
     <Compile Include="Speed\ArcARC.cs" />
     <Compile Include="Stack\ArcGPK.cs" />
+    <Compile Include="StudioJikkenshitsu\ArcUMPK.cs" />
     <Compile Include="StudioJikkenshitsu\ImageDAT.cs" />
+    <Compile Include="StudioJikkenshitsu\ImageGRC.cs" />
     <Compile Include="StudioJikkenshitsu\ImageGRD.cs" />
     <Compile Include="StudioJikkenshitsu\SjTransform.cs" />
     <Compile Include="StudioJikkenshitsu\WidgetSJDAT.xaml.cs">
diff --git a/ArcFormats/CatSystem/ArcDAT.cs b/ArcFormats/CatSystem/ArcDAT.cs
new file mode 100644
index 00000000..bc574d79
--- /dev/null
+++ b/ArcFormats/CatSystem/ArcDAT.cs
@@ -0,0 +1,127 @@
+//! \file       ArcDAT.cs
+//! \date       2019 Mar 11
+//! \brief      Cat System resource archive.
+//
+// Copyright (C) 2019 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.Text;
+
+namespace GameRes.Formats.CatSystem
+{
+    [Export(typeof(ArchiveFormat))]
+    public class DatOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DAT/CSPACK"; } }
+        public override string Description { get { return "Cat System resource archive"; } }
+        public override uint     Signature { get { return 0x61507343; } } // 'CsPack2'
+        public override bool  IsHierarchic { get { return false; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            if (!file.View.AsciiEqual (0, "CsPack2"))
+                return null;
+            uint data_offset = file.View.ReadUInt32 (8);
+            const int entry_size = 24;
+            int count = (int)(data_offset - 12) / entry_size;
+            if (!IsSaneCount (count))
+                return null;
+
+            var dir = new List<Entry> (count);
+            uint next_offset = data_offset;
+            var name_decoder = new CsNameDecryptor (0x1E);
+            var entry_buffer = new byte[entry_size];
+            int index_pos = 12;
+            for (int i = 0; i < count; ++i)
+            {
+                file.View.Read (index_pos, entry_buffer, 0, entry_size);
+                var name = name_decoder.Decrypt (entry_buffer);
+                var entry = Create<Entry> (name);
+                entry.Offset = next_offset;
+                next_offset = entry_buffer.ToUInt32 (0)
+                            ^ entry_buffer.ToUInt32 (4)
+                            ^ entry_buffer.ToUInt32 (entry_size - 4);
+                entry.Size = (uint)(next_offset - entry.Offset);
+                if (!entry.CheckPlacement (file.MaxOffset))
+                    return null;
+                dir.Add (entry);
+                index_pos += entry_size;
+            }
+            return new ArcFile (file, this, dir);
+        }
+    }
+
+    internal class CsNameDecryptor
+    {
+        int             m_name_length;
+        byte[]          m_buffer;
+        StringBuilder   m_name;
+
+        public CsNameDecryptor (int name_length)
+        {
+            m_name_length = name_length;
+            m_buffer = new byte[m_name_length];
+            m_name = new StringBuilder (m_name_length);
+        }
+
+        public string Decrypt (byte[] buffer)
+        {
+            int length = m_name_length / 6 * 4;
+            int dst = 0;
+            for (int pos = 0; pos < length; pos += 4)
+            {
+                uint num = buffer.ToUInt32 (pos);
+                for (int i = 5; i >= 0; --i)
+                {
+                    uint val = num % 40;
+                    num /= 40;
+                    m_buffer[dst+i] = (byte)val;
+                }
+                dst += 6;
+            }
+            m_name.Clear();
+            AppendChars (0, m_name_length - 4);
+            if (m_buffer[0x10] != 0)
+            {
+                m_name.Append ('.');
+                AppendChars (0x10, 3);
+            }
+            return m_name.ToString();
+        }
+
+        const string Alphabet = "_0123456789abcdefghijklmnopqrstuvwxyz_";
+
+        void AppendChars (int pos, int length)
+        {
+            for (int i = 0; i < length; ++i)
+            {
+                if (0 == m_buffer[pos+i])
+                    break;
+                m_name.Append (Alphabet[m_buffer[pos+i]]);
+            }
+        }
+    }
+}