To experiment with the Kindle lending library, I am enrolling Fairy Metal Thunder in KDP Select. This means that it will be exclusively available on Kindle for 90 days (include Kindle apps like Kindle for PC, etc.).
If you've already started the series on another platform, don't worry--the second book in the series, as well as the third one coming out this spring, will continue to be available on all platforms. Only the first book will be exclusive to Kindle.
You still have today to grab Fairy Metal Thunder on Nook and other platforms. After that, you would need a Kindle or Kindle app to read it during the next three months.
So, that's what's happening with that, and very soon.