"Sengoku Youko" is set in a fantastical version of Japan's Sengoku period, blending historical elements with supernatural themes. The narrative revolves around Tama, a fox spirit (youko) who despises humans, and her adoptive brother Jinka, a human who aspires to become a demon. Together, they embark on a journey to protect humans from malevolent spirits, despite Tama's initial disdain for them. Their mission is complicated by their contrasting ideologies: Tama seeks to eradicate evil spirits to protect humans, while Jinka desires to harness their power to become stronger.

The story introduces a variety of characters, including Shinsuke, a young swordsman who joins Tama and Jinka on their quest. Shinsuke's journey intertwines with theirs as he seeks to avenge his family, which was destroyed by demons. The trio encounters numerous challenges, including battles with powerful spirits, political intrigue, and moral dilemmas. The narrative explores themes of coexistence between humans and spirits, the nature of good and evil, and the personal growth of its characters.

As the story progresses, the characters face increasingly complex conflicts, including encounters with the Hyouma, a group of humans who have transformed into demons to gain power. The Hyouma's leader, Senya, becomes a central antagonist, challenging the protagonists' beliefs and forcing them to confront their own limitations. The series delves into the backstories of its characters, revealing their motivations and the events that shaped their worldviews.

The plot is driven by a mix of action, strategy, and emotional depth, with the characters' relationships evolving as they navigate the chaotic world around them. The narrative balances episodic adventures with an overarching storyline, gradually building toward a climactic confrontation that tests the bonds between Tama, Jinka, and Shinsuke. The series concludes with a resolution that ties together the characters' arcs while leaving room for reflection on the themes of redemption, sacrifice, and the blurred lines between humanity and monstrosity.