The Tellius Games
Tellius is the GameCube and Wii continent: Path of Radiance (2005) and its direct sequel Radiant Dawn (2007). Between them sits the series' deepest treatment of race and empire: the human beorc and the shapeshifting laguz, nations built on each other's subjugation, and a goddess sleeping inside a medallion, the Fire Emblem of this world.
THE TWO GAMES
GameCube and Wii, 2005 and 2007
WHY TELLIUS STANDS APART
The console diptychTellius is the series' world-building peak. The laguz nations, bird, beast, and dragon tribes with their own politics, make the standard Fire Emblem map of kingdoms into a map of species, and both games keep asking who pays for whose freedom. Senri Kita's character art, documented on the art shelf, gives the two games a painted, heraldic look unlike anything before or since.
It is also a commercial hinge. Path of Radiance arrived late in the GameCube's life and sold well enough, provided a late boost, and reaffirmed Nintendo's faith in the series, per the series' documented history. Radiant Dawn's difficulty and the DS remakes' softer sales opened the lean years that ended, eventually, in Awakening's ultimatum.