Right in the first episode of "Buffy the Vampire Slayer", two facts are established: the barely 16-year-old girl we see on screen hunting vampires, failing to accomplish a new beginning in a different town, has a calling. She is the slayer.
"Into each generation a girl is born: one girl in all the world, a chosen one. She alone will wield the strength and skill to fight the vampires, demons, and the forces of darkness; to stop the spread of their evil and the swell of their numbers. She is the Slayer."Two: this is a different kind of slayer. From the prophecy, we assume that the slayer is alone. She deals with what it means to be THE slayer, not one among many, but THE one. She alone has the responsibility of, now and then, avoiding the apocalypse, in addition to the daily trade of patrolling the shady parts of Sunnydale, which is positioned right on the Hellmouth. But Buffy, in the first episode called "Welcome to the Hellmouth", finds friends who, upon finding out about the existence of vampires and demons, decide to join her ranks. Those are not the popular kids to whom Buffy, played by then 20-year-old Sarah Michelle Gellar, would more obviously belong if you only regarded the shiny surface. It is two geeks: Willow, a computer-nerd with an unsetting intelligence paired with a stunning social awkwardness, and Xander, a geeky guy who can barely express his feelings, much less his thoughts.
The first novel of the Harry-Potter-series appeared in the very same year as the first episode of Joss Whedon's "Buffy" aired, yet we would probably follow our gut feeling that Harry Potter owes more to Whedon than the other way round. For once, Harry Potter has, incidentally or not, the very same premise: the young boy here is alone when he starts out, even more than Buffy, since he has lost his parents and lives with his wacky uncle and aunt, he has no friends, and he is just finding out that he is more than an ordinary boy, possessing abilities way beyond of his Muggle surrounding: he is a wizard, and therefore invited to go to Hogwarts, which is a new place, just as Sunnydale is for Buffy.
His new-found friends resemble the Scoobies in an odd way: Hermione is the smart, bookwormy geek who is extremely helpful when doing research about the demon of the week, while Ron isn't exactly a genius wizard, yet has the heartwarming stupid bravery of those who are willingly going to put their lives in danger for us, if they can stand alone in a fight or not.
Admittedly, Harry Potter starts out years earlier. While Buffy deals with growing up, becoming an adult after an adventurous life as a teenager with a bit more than the next Saturday night to plan, Harry Potter is more about being a child without being granted the carelesness of childhoold, to becoming a teenager that really has to take the place of adults, who continously die or fail. Joss Whedon, consequently as he is with his toybox of doom, strips away everything from Buffy that might give her a save ground to stand on: her mom dies, her choice of boyfriends gets more questionable each time, while her responsibilities, from just slaying the occasional vampire to avoiding the apocalypse to taking care of her "sister" Dawn after her Mom dies so unexpectedly and sudden, just keep on growing. For Harry Potter, the responsibility is always the same: he alone realizes that Voldemort is on the rise again, and he alone, with his history of being the only one to ever survive an attack of He who shall must be named, can slay the man to bring about the end of humanity.
In both cases, the usualy instances of safety are unable to deal with the task. In the case of Sunnydale, the police and the general public have learned to deal with the demons and vampires with a mixture of supression and ironic ignorance, while the higher forces, such as the mayor, is a bit demony by itself. Buffy loses her Mom, eventually, not even her Watcher can really help her. In Harry Potter's case, he starts out with little anyway: without parents, and only the headmaster of his school to rely on, he loses the one source of security he gains as the story progresses: Sirius, his godfather, is cruelly killed by an evil, wacky with, and the headmaster soon meets the very same destiny, only after an entire novel is dedicated to establishing that the official government, led by Orwellian dictator character is morally questionable at best, completely ignoring the threat that is growing once again. The authority, and every single adult in Harry's life, is stripped away or unable to deal. The responsibility falls on him.
One of the central themes of "Buffy the Vampire Slayer" is whether or not the titular heroine is going to accept the initial prophecy or not. It is difficult to realize that she will never have a normal life, that her calling will always overshadow everything else (also, that Slayers tend to have very low life expectancy...) - and she sometimes bails out, running away, or just sacrificing herself for her sister, with, in retrospect, seems like an easy way out, especially after we find out that she was in a heavenly dimension and resented to be resurrected by her very own friends in the dark sixth season.
But, as I pointed out in the very first paragraph, this Slayer is different from those preceding her: she has friends, who she cares for and who, as they grow into their roles, find ways to be essential to her work. Willow becomes a witch, and Xander, in his geeky kind of way, is the guy to ground them in the real life, since he has no special abilities of any kind. Without the Scoobies, Buffy might be dead (especially since it was Xander, of all people, to reanimate her in the very first season, after she got drowned, something her Vampire protector Angel could not do for lack of essential breath). The same counts for Harry: the most precarious situations occur when the group falls apart, or when one element breaks away. In season six, the most terrifying moment for the gang happens when one of them turns into the most challenging villain so far: when Willow loses it after her lover Tara gets killed randomly, and she realizes her potential in the worst way possible by becoming a very dark and very powerful witch.
Both of those heroes realize slowly that there friends may as well be at the core of their success: Buffy is alive because of them, and again and again is saved from death (sometimes even literally) by them, although also against her will when she just wants to rest her bones. Harry Potter changes his destiny by not being alone, by being able to chose his own destiny rather the following some obscure, ancient prophecy. In both instances, the overcoming of an old, dusty prophecy is at the core: Buffy realizes that being the only one initially doesn't mean that it always has to be that way - she can spread the responsibility, the potential - and Harry Potter needs to rely on his core of friends, by the last book considerably larger than in the first, to fight the one true evil, Voldemort.
Both of those central, titular characters, are unable to lead a normal life. They fall in love, and their love interest eventual becomes the target of evil. Their family is usually in great danger, their friends are always involved in whatever it is that threatens, in the worst case scenario, they become the villains. But one thing is essential in both of these work of arts: without this circle, without this kind of intimacy, they would not be able to succeed in the end. While their lives are about responsibility and sacrifice, they need the safety and soundness of a small, but reliable, circle of friends. With this, they might just beat the prophecy that overshadows them.
Buffy the Vampire Slayer, 1997-2004, created by Joss Whedon, with Sarah Michelle Gellar, Alyson Hannigan, Nicholas Brendon, Anthony Stewart Head, James Marsters, Michelle Trachtenberg, Emma Caulfield, Amber Benson, Seth Green, Charisma Carpenter, Kristine Sutherland, David Boreanaz, Marc Blucas, Danny Strong, Tom Lenk, Eliza Dushku.
The Harry Potter Series, 1997-2007, written by J. K. Rowling.