While the game's called Three Houses, there's actually an alternate fourth path you can take. Here's how to unlock the Fire Emblem Three Houses fourth route.
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Fire Emblem Three Houses Guide - Which House Should You Pick First?
How to unlock the Alternative 4th Story Route with The Black Eagles in Fire Emblem: Three Houses - Gamepur
How To Unlock The SECRET 4TH PATH In Fire Emblem: Three Houses (MISSABLE / SPOILERS)
My Fire Emblem Three Houses Review (Black eagles route)
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Fire Emblem: Three Houses Trailer: «Welcome to the Black Eagle House» – Nintendo Switch. – NINtheorist
FIRE EMBLEM: THREE HOUSES - BLACK EAGLES 】Go on, Blind - 2nd Route MADDENING NG+
FIRE EMBLEM: THREE HOUSES - BLACK EAGLES 】 BE Blind - 2nd Route MADDENING NG+
How to unlock the Alternative 4th Story Route with The Black Eagles in Fire Emblem: Three Houses
Fire Emblem: Three Houses Secret Route Guide - Fourth Route, Requirements and More - Prima Games
Fire Emblem: Three Houses Walkthrough, Cheats, and Codes
FE3H, Silver Snow Chapter Story Walkthrough (Black Eagles - Church of Seiros Route)
FE3H, How to Unlock Edelgard Story Route (Fourth Story Route)