"The Wizarding World" Wizards and witches live in secrecy to ensure their true identities are not discovered by Muggles—ordinary people—while the order of the world is maintained under the laws of the Ministry of Magic.

Children with magical talent enter Hogwarts School of Witchcraft and Wizardry at the age of eleven to study magic for seven years. Before starting, they visit Diagon Alley, a wizarding shopping district, to gather necessary supplies such as wands, textbooks, uniforms, and potion ingredients.

At Hogwarts, students are sorted by the Sorting Hat into four houses: Gryffindor, Hufflepuff, Ravenclaw, and Slytherin. Gryffindor prizes courage; Hufflepuff values hard work and loyalty; Ravenclaw esteems wit and creativity; and Slytherin gathers those with ambition and strong will. Despite their differing values, the students grow alongside their peers, aiming to become fully-fledged wizards.

However, a great darkness is approaching this peaceful world. Lord Voldemort, the most powerful Dark Wizard in history, seeks to rule the wizarding world through pure-blood supremacy and has taken many lives. Out of fear, people avoid even speaking his name, referring to him as "He-Who-Must-Not-Be-Named." Furthermore, a "Taboo" curse has been placed on his name, creating the danger that anyone who speaks it will have their location revealed to the enemy.

In the wizarding world, the three "Unforgivable Curses"—Avada Kedavra (the Killing Curse), Crucio (the Torture Curse), and Imperio (the Control Curse)—are strictly forbidden. Additionally, using magic carelessly in front of Muggles or misusing Dark Arts is considered a serious crime, and strict laws exist to govern the community.

Now a sixth-year at Hogwarts, Harry Potter explores Voldemort's past with Headmaster Albus Dumbledore and learns of the existence of "Horcruxes," the secret to the Dark Lord's immortality. Meanwhile, his classmate Draco Malfoy is ordered to carry out a dangerous mission, and the shadows of war creep into Hogwarts. The once-peaceful school life begins to crumble, and as the bonds between friends and their respective resolves are tested, a tragedy that will decide the fate of the wizarding world begins to unfold.

The Dark Mark is a magical brand etched only upon the Death Eaters who have sworn loyalty to Lord Voldemort.

The design of the Mark depicts a large human skull with a serpent emerging from its mouth like a tongue. The snake is a symbol of Voldemort himself, and the mere sight of this Mark strikes terror into the hearts of many wizards.

The Death Eater's Mark is typically branded on the inner forearm of the left arm. Usually, it looks like a faint, dark bruise or tattoo, but when Voldemort summons his Death Eaters or when his power grows, the Mark burns jet black, becoming hot and painful to the touch. Furthermore, Death Eaters can send a signal to Voldemort by touching their own Mark, or conversely, receive a summons from him.

Additionally, the term "Dark Mark" can refer to the massive magical sign of a skull and serpent cast into the sky. This is fired into the air following a murder or an attack, serving as a terrifying signpost to show that the deed was the work of Voldemort or his Death Eaters.

And yet, there is one within the school suffering because of that Mark...

And it is a secret that must never be known by the school or anyone else.