diff --git a/animetosho2mks.py b/animetosho2mks.py
new file mode 100755
index 0000000..fc5aaa9
--- /dev/null
+++ b/animetosho2mks.py
@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+from subprocess import run
+from tqdm import tqdm
+import glob
+import mimetypes
+import os.path
+
+
+class SubtitleTrack:
+    def __init__(self, filename):
+        self.filename = filename
+        self.language = self._parse_filename()
+
+    def _parse_filename(self):
+        basename = self.filename.split(".")[0]
+        language = basename.split("_")[1]
+
+        return language
+
+
+class Attachment:
+    def __init__(self, filename):
+        self.filename = filename
+        self.mimetype = mimetypes.guess_type(self.filename)[0]
+        if self.mimetype is None:
+            raise Exception(f"Cannot guess mimetype of attachment {self.mimetype}")
+
+
+class AnimeToshoFile:
+    def __init__(self, base):
+        self.base = base
+        self.outfile = os.path.splitext(self.base)[0] + ".mks"
+        self.subtitle_tracks = list(map(SubtitleTrack, self._relative_glob("*.ass")))
+        self.attachments = list(map(Attachment, self._relative_glob("attachments/*")))
+        self.chapters = "chapters.xml"
+        if not os.path.isfile(os.path.join(self.base, self.chapters)):
+            self.chapters = None
+
+    def _relative_glob(self, pattern):
+        for file in glob.glob(os.path.join(glob.escape(self.base), pattern)):
+            yield os.path.basename(file)
+
+    def _full_path(self, filename):
+        return os.path.join(self.base, filename)
+
+    def merge(self):
+        command = ["mkvmerge", "-q", "-o", self.outfile]
+        if self.chapters:
+            command.extend(["--chapters", os.path.join(self.base, "chapters.xml")])
+        for subtitle_track in self.subtitle_tracks:
+            command.extend(
+                [
+                    "--language",
+                    f"0:{subtitle_track.language}",
+                    os.path.join(self.base, subtitle_track.filename),
+                ]
+            )
+        for attachment in self.attachments:
+            command.extend(
+                [
+                    "--attachment-mime-type",
+                    attachment.mimetype,
+                    "--attach-file",
+                    os.path.join(self.base, "attachments", attachment.filename),
+                ]
+            )
+
+        run(command, check=True)
+
+
+for file in tqdm(list(map(AnimeToshoFile, glob.glob("*.mkv")))):
+    file.merge()