Eternal Darkness: Sanity's Requiem (Nintendo Cinematic Universe)

Eternal Darkness: Sanity's Requiem is a Japanese graphic novel.

Summary
Inheriting a mansion in Rhode Island from from her grandfather, Alexandra Rovias learns of its dark secrets by reading a book known as the Tome of Eternal Darkness.

Plot Elements

 * In 2000 AD, Alexandra Roivas finds herself returning to her family's estate in Rhode Island after her grandfather, Edward Roivas, her only living relative, is found brutally murdered.
 * Two weeks after returning, with the local police having gotten nowhere with the investigation, Alex decides to investigate the mansion for clues, and stumbles upon a secret room containing a book bound with human skin called the Tome of Eternal Darkness. Deciding to read it, she finds it contains accounts of various people in the past, beginning with the story of Pious Augustus.
 * Pious Augustus, a respected Roman military commander, is sent to Ancient Persia to locate an important relic.
 * Lured away from his men by mysterious voices, Pious finds himself venturing into an underground temple complex called the Forbidden City. He comes across three artifacts. Each possessing the essence of a powerful godlike being referred to as "Ancients".
 * Upon attempting to touch one of the artifacts, Pious finds himself corrupted by its power, whereupon he pledges his allegiance to the artifact's Ancient and begins working on summoning them into the universe.
 * The remaining two artifacts that Pious did not claim are put out of Pious' reach. One of the other artifacts represents the Ancient that is stronger than Pious', and the other represents the Ancient weaker than Pious'.
 * The artifact representing the weaker Ancient remained in the Forbidden City.
 * A young Persian swordsman named Karim, ventures to the Forbidden City to locate a treasure for a woman that he loves. Upon finding it, he sacrifices himself in order to guard it. Pious returns to Persia in the Middle Ages to construct a Pillar of Flesh at the Forbidden City, as part of his master's plans.
 * Roberto Bianchi, a Venetian architect traveling through the region, is captured by Pious' men. While under involuntary servitude, he encounters the spirit of Karim, who entrusts him with the artifact in his possession.
 * Soon after, Roberto is buried alive, along with many others, under tons of concrete.
 * Centuries later, a Canadian firefighter named Michael Edwards works with his team to extinguish several major oil fires in the Middle East, following the end of the Gulf War. After an explosion killed his entire team and trapped him in the Forbidden city, he is approached by Roberto's spirit, who gives him the artifact and instructs him to take it to the Roivas Family Estate.
 * Michael then moves to destroy the Forbidden City with a magickally enhanced bomb.
 * A few months later, Michael delivers the artifact to Edward Roivas in secret, telling him that he "won't last a night."
 * Meanwhile, the artifact representing the stronger Ancient is moved, by Pious, to Oublié Cathedral, in Amiens France, in order to prevent it from being used against him.
 * First, though, Pious orders the assassination of Charlemagne the Frank, so his movement cannot impede his plans. A Frankish messenger named Anthony, who stumbles upon the plot, travels to the then small monastery in order to warn him of the danger to his life. Despite Anthony's best efforts, he arrives too late to save him and dies from the spell he was afflicted with.
 * When the location is a newly constructed Cathedral, Pious Augustus summons a creature called the Black Guardian, to protect the artifact that could defeat his master.
 * A Franciscan monk named Paul Luther, visiting the region to view a holy relic at the cathedral, finds himself accused of murdering a fellow monk by the local Inquisition. Attempting to clear his name, he encounters the Black Guardian, which promptly kills him.
 * During World War I, Oublié Cathedral is converted into a field hospital.
 * Peter Jacob, a field reporter making accounts about the war, notes that patients have been disappearing of late. Venturing into the catacombs, he finds himself encountering the Black Guardian and defeats it, recovering the artifact it was guarding.
 * Sixty-nine years later, Edward is visited by a now elderly Peter Jacob who gives an account of his experience in Amiens before handing over the artifact in his possession.
 * While the other two artifacts are fought over between Pious and several unwitting souls, the "Corpse God" Mantorok, another powerful god-like being that can oppose Pious' master, has an artifact of its own.
 * In the Middle Ages, Pious travels to a temple in Angkor Thom, Cambodia in order to deal with Mantorok.
 * A young Khmer slave girl, named Ellia, finds herself trapped within the temple at the same time. While trying to find her way out, she is approached by one of Mantorok's servants, who entrusts her with the task of protecting the Ancient's essence within her body. Pious kills her shortly after.
 * Centuries later, Dr. Edwin Lindsey, a noted archaeologist, ventures to Cambodia on an expedition to visit a hidden temple complex. After nearly being killed by Pious, who disguised himself in order to accompany him, Edwin finds Ellia's body and is entrusted by her spirit with Mantorok's essence, which he eventually delivers to Edward a few weeks later.
 * Alongside the struggle to claim the powerful artifacts of the Ancients, the Roivas Family Estate in Rhode Island, USA holds secrets of its own.
 * Dr. Maximillian Roivas, a colonial ancestor of Alex and her grandfather, inherits his father's mansion in Rhode Island and decides to investigate its secrets. He soon finds a large cavern beneath the mansion, containing an ancient city within called Ehn'gha. He returns to the surface to get help, only to be considered delirious, and is sent to an asylum for the rest of his life.
 * In the middle of the 20th century, Dr. Edward Roivas, a clinical psychologist at the time, inherits the Estate. Finding his way underground, Edward discovers the city incorporates magick machinery and uses it to greatly damage the city with a powerful destructive spell. Knowing this is not enough, he decides to research what he can within the Tome for the final battle.
 * After a decades-long time skip, Edward is assassinated by one of Pious' servants.
 * Alexandra Roivas, having learned all she can from the Tome, decides to finish the fight. Recovering the artifacts from within the mansion, she soon ventures into Ehn'gha and uses them with the city's machinery, in order to summon a rival Ancient to fight Pious' master.
 * Alex then engages Pious in combat, aided by the spirits of those written in the Tome, eventually defeating him and destroying the essence of his master, who is defeated by its rival.
 * Edward's spirit then acts quickly to use Ehn'gha's mechanism to send back the summoned Ancient before it can cause any harm to the world.