Death's Daughter and the Ebony Blade (Manga) Volume 4 by Maito Ayamine

Fernest can’t seem to catch a break. Just when the Royal Army is riding high after Olivia’s incredible victories, the empire swoops in to crush their legions in the north. Now, nothing stands between the imperial army and the embattled Second Legion on the central front. Luckily, with the south back under Fernest’s control, Olivia and the Seventh Legion are free to ride to their aid! But Ashton has his misgivings, and they aren’t unfounded—lurking in the north is General Rosenmarie of the Crimson Knights. She’s hell-bent on revenge and wants nothing more than to see the whole of the Seventh Legion slaughtered. There’ll be plenty of enemies for Olivia to slice up, and even a princess to save, as she, Claudia, and Ashton set off on their latest mission.