Role in the Story
He first appears at the end of Chapter 21, when he arrives at the school. In Chapter 22, he is seen speaking to Albert Dumblydore with Doris Rumbridge. Angered by the threat of the Bark Lord to kill the students, the two Mystery officials inform Dumblydore that the school will have to be closed, adding that Dumblydore is no longer fit to be headmaster, as his "Alzheimer's is dangerous" and so he "must retry."
Dumblydore retorts that the school cannot be closed, and only one person can kill Voldemort...Ebony Dark'ness Dementia Raven Way. This conversation is overheard by Ebony, along with B'loody Mary, Vampire, Diabolo, Draco, Dracula and Willow. Cornelia leaves with Rumbridge, after which he disappears from the chapter's narrative.
He doesn't appear again until Chapter 36, where he is found by the students to have taken over as professor of Potions class. He tells the students to "STFU!1" and informs them that Dumblydore is now in Abkhazian with Snap and Loopin. He adds that Dumbyldore is "old and week" and has "kancer" (suggesting that retrying did nothing for Dumblydore's health). Despite his status as professor, the students talk amongst themselves, causing Cornelia to go into a rage and go for Rumbridge. Once again, he disappears from the story's narrative.
Cornelia is only mentioned one more time, in Chapter 42, when Professor Trevolry tells Ebony that he is coming to "help every1." Unfortunately, he is too late to appear in the fanfiction's awesome climax.
Difference from the Original
Cornelia Fuck is based off of Cornelius Oswald Fudge in the original books. He serves as the Minister of Magic, and only appears in regards to concerns of the Ministry, sometimes deferring various duties to inferiors (you know, like any government official does in reality). Unlike his prototype in the books, Cornelia appears to handle all matters himself, with no one under him to defer to, as if he's the only one in the entire Mystery aside from Doris. Even taking the role of a professor for one class appears perfectly fine for him to do, as if no one will require his role as minister.
Also unlike the original Cornelius, who only grew upset when pressed, Cornelia appears to be a loose cannon. Cornelia swears at students, telling them to shut up, and then, at just one student disobeying, leaves the room in a huff, yelling at the top of his lungs.
One important difference is that, while the original Cornelius initially refused to believe that Voldemort had returned and refused all of Dumbledore's advice, the Cornelia of My Immortal appears to not only readily accept that Voldemort is back and poses a danger, but he is the one giving advice on how to handle the situation.