Star Wars has finally revealed the truth about the Sith dagger seen in Star Wars: The Rise of Skywalker. The sequel trilogy is generally considered to have come to an unsatisfactory conclusion, in large part due to a lack of planning. A lack of synergy between the creative visions of directors J.J. Abrams and Rian Johnson also resulted in The Rise of Skywalker having numerous plot holes, and it has fallen to the franchise's canon tie-ins to try to fix them.
The film's Sith dagger was arguably the worst plot hole of all. It was said to be ancient, and it bore a Sith inscription written in ur-Kittât, a forbidden tongue in the Republic. The Sith dagger was designed to show a person the location of Palpatine's Sith Wayfinder - and it led Rey to the planet Kef Bir, one of the moons of the gas giant Endor. It pointed Rey to the wreckage of the second Death Star, to a hidden chamber where the Emperor had secreted this treasure. The Sith dagger just didn't make any sense, because it was somehow both old enough to be tied to the Sith Empire and yet new enough to guide Rey through the Death Star's wreckage.
The full story of the Sith dagger is finally revealed in Adam Christopher's novel Shadow of the Sith. Set before the events of the sequel trilogy, the book is focused on the story of Rey's parents and Ochi of Bestoon's pursuit of them. Ochi had become obsessed with locating the Sith redoubt of Exegol, which he believed was the key to conquering death itself. The Sith Eternal gave him the dagger, promising it would guide him to Exegol once he had completed his mission and captured Rey and her parents. The blade itself was ancient, but Ochi of Bestoon noticed its serrated edges were bright, "like they were freshly machined." Presumably, the inscription was added as well, with the Sith Eternal planning to translate it for Ochi when his mission was complete.
The Sith dagger was soaked in the dark side of the Force, hungry for blood and exerting an influence on anyone who held it. Ochi of Bestoon made the mistake of using the Sith dagger to kill, and he grew increasingly bloodlusted. When Ochi finally captured Rey's parents, the blade's baleful influence meant he murdered them before attempting to interrogate them to find Rey. He made the mistake of going to Pasaana, following a red herring planted by Rey's mother, and met his end there.
This is the irony of the Sith; the dark side is both their strength and their weakness. It feeds on hatred and rage, but it also fuels it. The Sith Eternal gave Ochi of Bestoon a weapon that amplified his darkest impulses, and in so doing they unwittingly ensured he would fail in his mission. If not for that Sith dagger, Ochi may well have chosen to keep Rey's parents alive long enough to figure out the girl was not on Pasaana, and he would surely have managed to break them in the end. Instead, he killed them, and unwittingly doomed Palpatine's plans in the Star Wars sequel trilogy.
