diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index 26b14718..d311cf08 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -120,6 +120,7 @@
     <Compile Include="elf\ImageRMT.cs" />
     <Compile Include="HuffmanCompression.cs" />
     <Compile Include="Lambda\ArcLAX.cs" />
+    <Compile Include="Maika\ArcBK.cs" />
     <Compile Include="Nexas\ArcTPF.cs" />
     <Compile Include="LiveMaker\ImageGALX.cs" />
     <Compile Include="Otemoto\ArcTLZ.cs" />
diff --git a/ArcFormats/Maika/ArcBK.cs b/ArcFormats/Maika/ArcBK.cs
new file mode 100644
index 00000000..6ca20902
--- /dev/null
+++ b/ArcFormats/Maika/ArcBK.cs
@@ -0,0 +1,150 @@
+//! \file       ArcBK.cs
+//! \date       2018 Jan 02
+//! \brief      MAIKA 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 GameRes.Compression;
+
+namespace GameRes.Formats.Maika
+{
+    [Export(typeof(ArchiveFormat))]
+    public class BkOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DAT/BK"; } }
+        public override string Description { get { return "Maika resource archive"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return true; } }
+        public override bool      CanWrite { get { return false; } }
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            uint index_offset = file.View.ReadUInt32 (0);
+            uint index_size = file.View.ReadUInt32 (4);
+            if (index_offset+index_size != file.MaxOffset)
+                return null;
+            using (var input = file.CreateStream (index_offset, index_size))
+            using (var packed = new PackedStream<LzBitsDecompressor> (input))
+            using (var index = new BinaryStream (packed, file.Name))
+            {
+                int count = index.ReadInt32();
+                if (!IsSaneCount (count))
+                    return null;
+                var dir = new List<Entry> (count);
+                for (int i = 0; i < count; ++i)
+                {
+                    uint offset         = index.ReadUInt32();
+                    uint size           = index.ReadUInt32();
+                    uint unpacked_size  = index.ReadUInt32();
+                    var name = index.ReadCString (0x104);
+                    var entry = FormatCatalog.Instance.Create<PackedEntry> (name);
+                    entry.Offset        = offset;
+                    entry.Size          = size;
+                    entry.UnpackedSize  = unpacked_size;
+                    if (!entry.CheckPlacement (file.MaxOffset))
+                        return null;
+                    if (name.HasExtension (".gpt"))
+                        entry.Type = "image";
+                    entry.IsPacked = entry.Size != entry.UnpackedSize;
+                    dir.Add (entry);
+                }
+                return new ArcFile (file, this, dir);
+            }
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            Stream input = arc.File.CreateStream (entry.Offset, entry.Size);
+            var pent = entry as PackedEntry;
+            if (null == pent || !pent.IsPacked)
+                return input;
+            input = new PackedStream<LzBitsDecompressor> (input);
+            input = new LimitStream (input, pent.UnpackedSize);
+            if (entry.Name.HasExtension (".gpa"))
+                input = new XoredStream (input, 0xFF);
+            return input;
+        }
+    }
+
+    internal class LzBitsDecompressor : Decompressor
+    {
+        MsbBitStream        m_input;
+
+        public override void Initialize (Stream input)
+        {
+            m_input = new MsbBitStream (input, true);
+        }
+
+        protected override IEnumerator<int> Unpack ()
+        {
+            var frame = new byte[0x400];
+            int frame_pos = 1;
+            for (;;)
+            {
+                int bit = m_input.GetNextBit();
+                if (-1 == bit)
+                    yield break;
+                if (bit != 0)
+                {
+                    int v = m_input.GetBits (8);
+                    if (-1 == v)
+                        yield break;
+                    m_buffer[m_pos++] = frame[frame_pos++ & 0x3FF] = (byte)v;
+                    if (0 == --m_length)
+                        yield return m_pos;
+                }
+                else
+                {
+                    int offset = m_input.GetBits (10);
+                    if (-1 == offset)
+                        yield break;
+                    int count = m_input.GetBits (5);
+                    if (-1 == count)
+                        yield break;
+                    count += 2;
+                    while (count-- > 0)
+                    {
+                        byte v = frame[offset++ & 0x3FF];
+                        m_buffer[m_pos++] = frame[frame_pos++ & 0x3FF] = v;
+                        if (0 == --m_length)
+                            yield return m_pos;
+                    }
+                }
+            }
+        }
+
+        #region IDisposable Members
+        bool m_disposed = false;
+        protected override void Dispose (bool disposing)
+        {
+            if (disposing && !m_disposed)
+            {
+                m_input.Dispose();
+                m_disposed = true;
+            }
+        }
+        #endregion
+    }
+}