Academy City, Japan, is at the forefront of science. Besides being 30 years ahead of the world technologically, more than three-fourths of this peculiar city's population consists of students developing their psychic abilities as espers in various institutions. Among these students is Touma Kamijou, a high school boy with the lowest psychic rank of zero, but with a mysterious power no scientist can understand: Imagine Breaker, which allows him to negate other supernatural abilities. This, however, doesn't affect Kamijou's life in the least as he plays his role as a regular teenager; that is, until he meets the strange Index Librorum Prohibitorum, a young girl who has memorized the entirety of the forbidden grimoires, and now a dangerous organization is hunting Index down. With several magicians looking to harm the girl, Kamijou will defend his new companion at all costs as he discovers a strange new realm of the supernatural.

Fear, survival, instinct. Thrown into a foreign land with nothing but hazy memories and the knowledge of their name, they can feel only these three emotions resonating deep within their souls. A group of strangers is given no other choice than to accept the only paying job in this game-like world—the role of a soldier in the Reserve Army—and eliminate anything that threatens the peace in their new world, Grimgar. When all of the stronger candidates join together, those left behind must create a party together to survive: Manato, a charismatic leader and priest; Haruhiro, a nervous thief; Yume, a cheerful hunter; Shihoru, a shy mage; Moguzo, a kind warrior; and Ranta, a rowdy dark knight. Despite its resemblance to one, this is no game—there are no redos or respawns; it is kill or be killed. It is now up to this ragtag group of unlikely fighters to survive together in a world where life and death are separated only by a fine line.

In the previous century, an unprecedented disaster known as the Invertia drastically reformed the world. The powers of existing nations declined significantly, paving the way for a conglomerate called the Integrated Empire Foundation to assume control. But more importantly, the Invertia led to the emergence of a new species of humans who are born with phenomenal physical capabilities—the Genestella. Its elite are hand-picked across the globe to attend the top six schools, and they duel amongst themselves in entertainment battles called Festas. Ayato Amagiri is a scholarship transfer student at the prestigious Seidoukan Academy, which has recently been suffering from declining performances. Through a series of events, he accidentally sees the popular Witch of Resplendent Flames, Julis-Alexia von Riessfeld, half-dressed! Enraged, Julis challenges him to a duel for intruding on her privacy. After said duel is voided by the student council president, Ayato reveals that he has no interest in Festas. Instead, he has enrolled in the academy to investigate the whereabouts of his missing elder sister. But when a more devious plot unravels, Ayato sets out to achieve victory, while being surrounded by some of the most talented Genestella on the planet.

Running into your new stepsister in the bathroom is not the best way to make a good first impression, which Basara Toujou learns the hard way. When his father suddenly brings home two beautiful girls and introduces them as his new siblings, he has no choice but to accept into his family the Naruse sisters: busty redhead Mio and petite silver-haired Maria. But when these seemingly normal girls reveal themselves as demons—Mio the former Demon Lord's only daughter and Maria her trusted succubus servant—Basara is forced to reveal himself as a former member of a clan of Heroes, sworn enemies of the demons. However, having begun to care for his new sisters, Basara instead decides to protect them with his powers and forms a master-servant contract with Mio to keep watch over her. With the Heroes observing his every move and the constant threat of hostile demons, Basara has to do the impossible to protect his new family members. Moreover, the protector himself is hiding his own dark secret that still haunts him to this day...