High school biology teacher Tetsuo Takahashi may look like your average everyday instructor, but beneath his gentle appearance lies something less ordinary: his fascination for the Ajin, more commonly known as Demi. Although these half-human, half-monster beings have integrated into human society, Takahashi believes that much about them will remain unknown unless he interacts with them firsthand. Demi-chan wa Kataritai follows Takahashi's daily life in Shibasaki High School together with his three Demi students—Hikari Takanashi, an energetic vampire; Kyouko Machi, a gentle dullahan; and Yuki Kusakabe, the shy snow woman. Along the way, Takahashi also meets fellow teacher Sakie Satou, a succubus with an aversion towards men. To fulfill his goal of learning more about the Demi, Takahashi decides to conduct casual interviews with the girls to learn more about their abilities, psyche, and interaction with human society. As Takahashi strengthens his bond with his students, he soon discovers that the Demi are not as unusual as he initially believed.

For Kanade Amakusa, life as a high schooler should have been normal, and it would have been—if he wasn't living with the most ridiculous curse imaginable. Absolute Choice, a system forced upon him by a self-proclaimed god, randomly presents a mental selection of actions that he must act out based on his choice. To add to his dilemma, it tends to occur in the most public of places, and his options never seem to deviate from the rude and crude in nature. As a result, the helpless boy stresses through each day, fumbling to repair his already tarnished reputation while desperately praying to avoid the next spontaneous episode of Absolute Choice. To his dismay, the one in charge is always one step ahead of him and proceeds to not-so-subtly choice him into the lives of several girls at his school. Just when Kanade's school life can't seem to be doomed any further, a decision that he reluctantly selects on the way home sends a beautiful girl crashing down from the sky, along with the promise of more hysterically hellish choices.

High school student Yuuichi Katagiri cherishes his close circle of friends, composed of four classmates: Yutori Kokorogi, Shiho Sawaragi, Makoto Shibe, and Tenji Mikasa. However, when the funds for the upcoming school trip are stolen, the incident causes Shiho and Makoto—who had been tasked with collecting the money—to distance themselves from the rest of their class. Soon after, Yuuichi and his friends are deceived into meeting up and knocked unconscious by unknown assailants. After waking, the group find themselves confined in a white room with controversial figure Manabu-kun, who reveals that one of the five has gathered them together to clear their personal debt of twenty million yen. To pay off the amount, they must participate in a variety of psychological games that will test the true nature of their friendship and humanity. Distressed and isolated from the outside world, Yuuichi and his friends need to cooperate to complete the games. But as their concealed feelings and problematic pasts begin to surface, their seemingly unbreakable bond may soon shatter into irreparable pieces.

Shidou Itsuka carries on with his quest for Ratatoskr in finding Spirits and trying to seal their powers, all while maintaining his relationships with the ones he had already sealed. Moreover, as new Spirits appear, he must undergo more complicated trials—all to put a stop to further disasters as he discovers more about the Spirits' origin.