If I decide to continue my storybook after class ends, I would write a story for each of the remaining Persona 5 characters: Mona (you got a Mona introduction, but no Mona story), Noir, Panther, Oracle and Queen. I decided to start doing some research and reading about their personas. I also located a few sources that might be useful for writing their stories.
Noir: Milady - Milady de Winter, more commonly referred to as "Milady" is a fictional character created by Alexandre Dumas for his seminal novel The Three Musketeers. Her main relation with the novel's titular heroes is her personal vendettas first against the novel's hero d'Artagnan after he discovered she was branded as a criminal with a fleur-de-lis, then against his mentor Athos who was her former husband. Her conflict with them ends in her death by beheading for her crimes. In both the book and subsequent adaptations, Milady is depicted as a fiercely independent and manipulative villain: despite acting as an agent of Cardinal Richelieu in his machinations against Louis XIII and the Duke of Buckingham, she is also a force on her own account, bringing others to ruin for personal gain. Her moniker of "Milady" is a title inherited from one of her husbands, whom she married under a false name, leaving her true identity a mystery.
Panther: Carmen - a fictive female gypsy created by Prosper Mérimée. She first appeared in Mérimée's eponymous novella that was first written and published in 1845. The novella was adapted into a variety of different genres, most notably the opera Carmen by French composer Georges Bizet which diverges in significant points from Mérimée's original story. Whatever the version, Carmen is generally depicted as a classic femme fatale who would take advantage of her beauty and charm to make men fall for her but quickly break the relationship once she is bored of her wooer and then looks for the next victim. Carmen is also usually seen smoking tobacco because she had once been working in a tobacco factory. She is later slain by a spurned ex-lover driven to a jealous rage after she leaves him. Though she knew he would be fated to kill her, she declares that she would rather die than allow herself to be bound to the will of another and that "Carmen will always be free".
Oracle: Necronomicon - 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.
Queen: Johanna - based on Pope Joan, a legendary Medieval woman who reigned as pope for a short period, going against the Catholic Church's ingrained tradition of male popes. Though the story was widely believed for centuries, modern historians have found no evidence of her existence and believe the legend to be a work of fiction meant to discredit the church. Most versions of her story describe her as a talented and learned woman who disguised herself as a man, often at the behest of a lover. In the most common accounts, due to her abilities, she rose through the church hierarchy and was eventually elected pope. Her sex was revealed when she gave birth during a procession, and she died shortly after, either through murder or natural causes. The accounts state that later church processions avoided this spot, and that the Vatican removed the female pope from its official lists and crafted a ritual to ensure that future popes were male.
Possible Sources:
(Photos from Megami Tensei Wiki)