Sengoku Youko, Volume 5 (manga)

The world is divided into two factions: humans and monsters called katawara. Despite being a katawara, Tama loves humans and vows to protect them from evil, even if it means fighting her own kind. Her stepbrother Jinka, however, hates humans, despite mostly being one. The siblings are joined by a cowardly swordsman named Shinsuke, who wants to learn how to become strong.