Nightmare x Onmyoji ~Kindan no Paradox~ by Guilty Nightmare Project - Adult Sex Game

At first glance, the protagonist, Katsuragi Kuon, is just an ordinary schoolgirl, but, as a descendant of an onmyouji bloodline, she has another face, not an ordinary one: along with her father, Kimihiro, she banishes evil spirits.

One day, three people, who purified evil spirits in a different land, Shindou Setsuna, her sister Shindou Yuuka, and friend Kitakawa Touma, came to Kuon. They asked for help with solving the case of recent disappearances in the neighborhood of this city. While Kuon and her new comrades gathered information and exorcised malicious spirits, Kimihiro went to meet his acquaintance, whom he thought to hold important information.

At that time, enemies made their move. Due to their attacks, Setsuna and Yuuka were captured by the enemies, and Kimihiro was incapacitated. Kuon, who found out about the cult, leading the demons from the shadows, strongly decided to fight to save her father and Setsuna with her sister.

Sure enough, you may already know, what awaits her at the end of her struggles...