Kojou Akatsuki's days as an ordinary high school student in the Demon District of Itogami Island come to an abrupt end after a fateful encounter leaves him with the remarkable abilities of a vampire. It isn't long before he is thrust into the center of attention when it is discovered that he is the fourth primogenitor, an immensely powerful vampire whom most consider to be merely a legend. Fearing Kojou's destructive potential, the Lion King Organization sends in an apprentice sword-shaman, Yukina Himeragi, to monitor, and should he become a threat, kill the boy deemed the world's most powerful vampire. Forced together by circumstance, the two form an unlikely alliance as Kojou comes to terms with his abilities and they both struggle to protect the city from various emerging chaotic forces.

On May 1, 1945 in Berlin, as the Red Army raises the Soviet flag over the Reichskanzlei, a group of Nazi officers conduct a ritual. For them, the slaughter in the city is nothing but the perfect ritual sacrifice in order to bring back the Order of the 13 Lances, a group of supermen whose coming would bring the world's destruction. Years later, no one knows if this group of officers succeeded, or whether they lived or died. Few know of their existence, and even those who knew began to pass away as the decades passed. Now in December in the present day in Suwahara City, Ren Fujii spends his days at the hospital. Every night he sees the same dream: A guillotine. Murderers who hunt people, and the black clothed knights who pursue the murderers. He is desperate to return to his normal, everyday life, but even now he hears his friend Shirō's words: "Everyone who remains in this city eventually loses their minds."

In Orario, fearless adventurers band together in search of fame and fortune within the underground labyrinth known as the Dungeon. But Bell Cranel, novice adventurer, has bigger plans than riches and glory; he fights monsters in the hope of having a fateful encounter with a girl. When this happens, it doesn't go exactly as he planned. Thus begins the story of an unlikely pair, a boy and a goddess, both trying to prove themselves, both eager to reach their goals.

After having descended upon this world, the gods have created guilds where adventurers can test their mettle. These guilds, known as "familia," grant adventurers the chance to explore, gather, hunt, or simply enjoy themselves.

The Sword Princess, Ais Wallenstein, and the novice mage, Lefiya Viridis, are members of the Loki Familia, who are experts at monster hunting. With the rest of their group, they journey to the tower of Babel in hopes of exploring the dungeon underneath. Home to powerful monsters, the dungeon will fulfill Ais's desire to master her sword skills, while bringing Lefiya closer to her dream of succeeding Riveria Ljos Alf, vice-captain of the Loki Familia, as the most powerful mage in the land.

In the Holy Grail War, seven magi chosen by the Holy Grail itself must summon seven Heroic Spirits to compete for the omnipotent Grail, a magical device that grants the victor any wish they desire. After three inconclusive wars, the fuse has now been lit once again for the fourth time.

Shirou Emiya lost his parents in a fire when he was young and was later adopted by the sorcerer Kiritsugu Emiya. Shirou is drawn into the Holy Grail War summons a female "Servant" known as Saber to protect him and obtain the Holy Grail.

This story focuses primarily on the heroine Rin Tohsaka. After her father’s death, Rin enters the Holy Grail War as the sole heir to the prestigious Tohsaka Household, with her servant Archer. But, she soon finds out that Shirou Emiya, a boy from her high school has gotten himself involved in the battles and unexpectedly saves him when he is fatally injured. Before long, Rin sets out to strike down the conspiracies surrounding the Holy Grail War along with Shirou and his summoned servant Saber. And so, the story begins to explore the truth behind Shirou’s powers and the nature behind his unyielding will to become a “hero.”