The Tome of Eternal Darkness is an ancient text of unknown origin at the center of Eternal Darkness: Sanity's Requiem. Bound in human flesh and bone, it chronicles the lives of those that come to possess it while also granting them the magical powers found within. Those that it chooses are capable of reading its text no matter what languages they speak. However, the lives of those that find it more often than not end in horrific death or madness.
Some characters, such as Ellia, acquire the tome at or near the start of their adventure, allowing them to use magic for most of their stages. However, others, such as Michael Edwards, don't find the tome until significantly later, forcing them to contend with monstrous adversaries with man-made weapons for a larger stretch of time.