diff --git a/Legacy/Gsx/ImageK4.cs b/Legacy/Gsx/ImageK4.cs
new file mode 100644
index 00000000..93c3dca8
--- /dev/null
+++ b/Legacy/Gsx/ImageK4.cs
@@ -0,0 +1,75 @@
+//! \file       ImageK4.cs
+//! \date       2019 Feb 07
+//! \brief      Toyo GSX image format.
+//
+// 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.ComponentModel.Composition;
+using System.IO;
+using System.Windows.Media;
+
+// [030825][Mirai] Hoshi no Oujo
+
+namespace GameRes.Formats.Gsx
+{
+    internal class K4MetaData : ImageMetaData
+    {
+        public bool HasAlpha;
+        public int  FrameCount;
+    }
+
+    [Export(typeof(ImageFormat))]
+    public class K4Format : ImageFormat
+    {
+        public override string         Tag { get { return "K4"; } }
+        public override string Description { get { return "Toyo GSX image format"; } }
+        public override uint     Signature { get { return 0x0201344B; } } // 'K4'
+
+        public override ImageMetaData ReadMetaData (IBinaryStream file)
+        {
+            var header = file.ReadHeader (0x10);
+            if (!header.AsciiEqual ("K4"))
+                return null;
+            if (header[2] != 1 || header[3] != 2)
+                return null;
+            return new K4MetaData {
+                Width  = header.ToUInt16 (4),
+                Height = header.ToUInt16 (6),
+                BPP    = header[0xF],
+                HasAlpha = header[0xB] != 0,
+                FrameCount = header.ToUInt16 (0xC),
+            };
+        }
+
+        public override ImageData Read (IBinaryStream file, ImageMetaData info)
+        {
+            var meta = (K4MetaData)info;
+
+            return ImageData.Create (info, format, palette, pixels);
+        }
+
+        public override void Write (Stream file, ImageData image)
+        {
+            throw new System.NotImplementedException ("K4Format.Write not implemented");
+        }
+    }
+}