Hi everyone! Just wanted to let the curious know that amazon.co.jp has listed the Complete Fire Emblem Fates Strategy Guide for release on July 15th for 1,944 Yen (~16 USD). You can import these for just 10 or so US dollars and they deliver rather fast. I am importing one myself to iron out recruitment methods as well as to make more in depth chapter data, and eventually a guide on gameFAQs with this handy source!
It says it includes everything you need to know about the Invisible Kingdom path as well as My Castle, among other things!