Marianne and the Forbidden Codex: A Fire Emblem Three Houses story

Marianne von Edmund, a student at the Officers' Academy, has had to flee with all her classmates, after the invasion of the Garrech Mach Officers' Academy by the Adrestian Empire, led by its new Empress, Edelgard von Hresvelg.
On her way home, and after separating from her companions, Marianne is attacked by some bandits. It is there when she is rescued by an old friend from her childhood, Leonard. Marianne will discover a secret about her friend that could plunge the continent of Fódlan into a debacle.
Together, they will embark on an adventure across the continent of Fódland, especially in the territories of the Leicester Alliance, to prevent Leonard's secret from falling into the hands of both the empire and Those Who Slither in the Dark. They will be joined by some companions from the Golden Deer's house for this purpose.
In turn, Marianne will awaken a capacity in herself that she would never have expected to live: that of fighting for what she wants and deserves.
Disclaimer: This is a fanfic story set in the world of Fire Emblem: Three Houses with no purpose other than to present an alternate reality to the narrative of the game's own lore. It has no associated commercial purpose.
© 2019 Nintendo / INTELLIGENT SYSTEMS Co-developed by KOEI TECMO GAMES CO., LTD. Fire Emblem and Nintendo Switch are trademarks of Nintendo © 2019 Nintendo.
Illustration collected from the tumblr account of @mayomoyo.