MangaDex

Haken no Kouki Altina

Regis Ulrich is an incapable soldier; bad at both sword and archery, who passes the time by only reading books. While transferring to a remote region post, he meets a girl who turns out be the red hair and crimson eyed princess Altina, the wielder of the great sword "Grantneil Catoll." Despite being only fourteen years old, she was appointed to become the commander of the army in this remote region simply because she was the illegitimate child of the Emperor. However, she continues to pursue her dream of becoming Empress despite the circumstances that surround her. To achieve this goal, she asks Regis to become her tactician and stand alongside her against the obstacles that are sure to come.