Board Thread:Questions and Answers/@comment-37626510-20181125231151

I just rewatched the anime and I enjoyed it a lot. I wanted to dive a bit deeper into the universe by reading manga. I know there's several versions but this one seems like it's the "official" one. According to every source the manga has 18 volumes but even on BookWalker I can only find up to 16. Was this manga completly dropped or what's the status? I don't want to read 16 volumes just to not have an ending. 