After inheriting the company from their parents, siblings Yuuhi and Yuamu Oudou have started to work at Ultraterrestrial Trouble Solutions, an organization that hunts aliens. Although they have never encountered aliens before, Yuuhi is desperate to meet one as he believes that an alien has stolen his important item called the "Earthdamar." One day, while searching for extraterrestrial creatures, Yuuhi and Yuamu find a strange spot in the forest where many trees have fallen, forming a scenery similar to a crop circle. As they venture further, they discover a mysterious spaceship and enter it out of curiosity. To their surprise, they come across Yudias Velgear, an alien from the Velgear Star Cluster. As it turns out, Yudias is seeking to learn about Rush Duel—a card game popular among elementary school students—as he believes that it will save his home from a long war. With the siblings agreeing to teach Yudias about Rush Duel, they eventually realize that their first contact with an alien may not be a random coincidence.

Melphiera Marchalrayd, the daughter of a count, dedicates her time to researching the culinary possibilities of monster meat—a peculiar endeavor started by her late mother. By teaching the people of the Marchalrayd lands to prepare such exotic ingredients, Melphiera hopes to help stave off famine. Unfortunately, her unique tastes and intimate knowledge of monsters have led to her social isolation: few nobles interact with her willingly, disdainfully calling her the "Voracious Villainess." When a monster attack erupts at a royal banquet—where Melphiera has been sent to find a husband—Aristide Rogier du Galbraith, the younger brother of the crown prince, leaps to her aid. Due to his terrifying skill in slaying monsters, Aristide has earned the title of "Blood-Man Duke." Charmed by Melphiera's fearlessness and intriguing culinary prowess, Aristide soon declares his intent to propose. Together, Melphiera and Aristide, high society's most eccentric couple, strive to see beyond the cruel rumors and encourage each other's fascination with monsters and the art of preparing them.

The rural American west is the setting for this OVA, in which a bizarre and brutal attack on a NASA base in Arizona attracts the attention of a French secret service agent, Monsieur Lassar, when a dead CIA agent is found floating on the Seine in Paris. Lassar is convinced that these two events are related, and sets out to prove it. His investigation leads him to film star Lamia Vindaw and a vampire cult that may be far more vicious and dangerous than its eccentric exterior makes it seem.

Unaired episode 13 included with the Blu-ray release of .