"What denies you is an illusion... A curse put upon you by the heartless... You knew from the very beginning... And yet, you cowered in fear... Will you die as you are told...? Who will you obey...? Cursed words spat out by a seething illusion? Or the truth within your own soul? Contract...I am thou, thou art I...The forbidden wisdom has been revealed. No mysteries...no illusions shall deceive you any longer."
The Necronomicon, whose original name is Al Azif, is a fictional grimoire (tome of magic). It was first mentioned in the short story The Hound written by H. P. Lovecraft, but its exact origin is the subject of debate. The book subsequently also appeared in stories of Lovecraft's followers. The Necronomicon has since gained a cult following and various fake "replicas" of the book are circulating.
In the context of Lovecraft's works, the Necronomicon is a tome detailing the truth behind the various ancient cosmic beings that have inhabited Earth and continue to influence humans for their own ends. Written in the 8th century by the "mad Arab" Abdul Alhazred, it both functions as a means of imparting the forbidden knowledge of the ancient ones, and a source of danger as those who read it risk going mad from its knowledge.
"The grimoire which contains vital information of the Cthulhu mythos by Lovecraft. Its original name is Al Azif. It is said the book itself is alive."
—Persona 5 compendium
Necronomicon is Futaba Sakura's Initial Persona, formed when she regains her will to live and accepts a consenting Shadow Futaba. It is shaped like a UFO with a metallic Gargoyle statue crouching on its top. The UFO's exterior is decorated with lime green glyphs of various origins. Futaba is piloting from the inside. This Persona symbolizes Futaba's unknown power and vast reserves of knowledge.
Necronomicon is a Navigator Persona with a limited array of skills by itself. However, by progressing Futaba's Confidant, more abilities can be used through it, including ones that can aid in battle or ambushing Shadows.
In keeping up with the theme of theft of Persona 5, the design of the UFO is based on the infamous rumor that extraterrestrial visitors abduct living beings on the earth to their ship and conduct inhumane experiments. It is also analogous to Futaba's role as a data analyst and her social alienation.
The patterns on Necronomicon's UFO is identical to those of the glass patterns seen on the bridges of Futaba's Palace.
The squid-like tentacles that pull Futaba into Necronomicon are an allusion to Cthulhu, the most well known of the eldritch pantheon created by Lovecraft.
Unlike other initial Personas, Necronomicon is never called by name, not even in battle. There's only one instance where Necronomicon is called by name and that's in Persona 5 Strikers when talking to Futaba in the 11th of August, although it's not voiced.