The team at Duolingo have just released an article detailing some of the techniques they use to help you learn. Similar to WaniKani (and many of Duolingo’s other courses,) their learning methods are supported by education research and are interesting to read about.
The course seems to be broken into thematic sections, I believe other programs like Human Japanese  use a similar structure, or at least use Japanese culture to teach you Japanese.
The course is currently unreleased and available on iOS only. You can view the status of the course in the Incubator program .
hideki We are thrilled to announce that our Japanese course is now available on iOS. It’s coming to Android in a few weeks, and web will be next!
[Edit] The course has not been released, jumping to conclusions on my part. I have updated the post to reflect this.