This week, Japanese fans (and importers) can download the final DLC map (that has been announced) for Fire Emblem Fates.
The Invisible History is a two-part mission that occurs before the events of the main story and explains how three returning characters from Awakening ended up in the world of Fates.
Additionally, as its title eludes, it delves a bit into the history of the Invisible Kingdom, which the third route focuses on. As such, I personally recommend completing the third route before playing this mission.
Those who reach the mission’s end will earn a Fellblood Emblem (allows any male character to change to the Grandmaster class) and First Dragon Blood (allows any character to utilise Dragon Vein).
For those curious about the story, check out the story summary by Kirokan and script translation (up to the end of the first map) by teddybearyt!