Lead heroine Buffy Summers in Joss Whedon's TV show, Buffy the Vampire Slayer, shares a birthday with another character on the series who seemingly couldn't be further from the Slayer.
Buffy Summers (Sarah Michelle Gellar) became a pop culture icon after the show's release in 1997. Enjoying seven seasons of success on two different networks, Whedon's Buffy the Vampire Slayer etched itself into the history books due to its take on both the "monster of the week" style of TV show and elements of a classic, coming of age story. Woven into this mix was the inclusion of supernatural threats: vampires, demons, and more. The center of this constant battle between good and evil was Buffy Summers, a teenage girl who was chosen to fight the forces of darkness as the Slayer. She and her friends, known as the Scooby Gang, worked in tandem to keep the balance firmly on the good guys' side.
Buffy the Vampire Slayer season 2 saw big changes for Buffy. Not only were things beginning to heat up between the Slayer and her ensouled vampire boyfriend, Angel (David Boreanaz), but Angel's past was heralded by the arrival of Spike (James Marsters) and Drusilla (Juliet Landau) who landed in Sunnydale to stir up trouble for their old friend and the Slayer. The two couples held up opposite sides of the ongoing good vs. evil power struggle in fictional Sunnydale, California, but Drusilla and Buffy, specifically, seemed destined to collide. Drusilla and Buffy share the same birthday, January 19th, and while Buffy's birthday has been subject of some confusion, it's clarified in Buffy the Vampire Slayer season 2, episode 13, "Surprise". "Surprise" was a two-part episode airing on consecutive days; the second part, episode 14, "Innocence", rounded out a powerful narrative for Buffy when her world was completely upended after she lost her virginity to Angel and subsequently caused him to lose his soul.
Because there's so much happening in both "Surprise" and "Innocence", it's easy to lose track of the small details. Angel losing his soul and reverting to bolster Spike and Drusilla's unquenchable thirst for violence was a big deal not only for the TV show, but for Buffy. Left heartbroken, the Slayer found herself fighting not only her former lover, but a demon known as The Judge (Brian Thompson), who was brought to town in pieces as a birthday gift to Drusilla. While Buffy does emerge victorious, and promptly ends The Judge's short-lived reign of terror with a rocket launcher, the notion that she shares a birthday with an undeniably evil vampire is interesting. Not only that, but it seems enough to be coincidental at first. Interestingly, Buffy's character arc in later seasons gives her more common bonds with Drusilla.
In some capacity, a Slayer seems to be bonded with vampires who have killed Slayers, even if it's just macabre fascination. This is certainly true of Buffy and Spike, though could be more coincidental due to the murky nature of their relationship. Drusilla ends up killing Kendra (Bianca Lawson), the Slayer who was called after Buffy's death in Buffy the Vampire Slayer season 1, in another two part episode (season 2, episode 21, "Becoming (Part One)"). This could give Buffy a more vested interest in Drusilla—the aforementioned dark interest—but the more important overlap between the two characters is via their shared romantic history. Drusilla and Spike are a long-term couple who have been off-again, on-again throughout the years; Spike ends up developing a romantic relationship with Buffy in Buffy the Vampire Slayer season 6. Drusilla also had a history with Angel, Buffy's beau in season 2.
Buffy the Vampire Slayer is full of minute details, plot holes, and other fun tidbits for its audience, which speaks to Joss Whedon's sensibilities as a writer. There's a reason why the show has been successful more than 20 years after release — whether being enjoyed by old fans or a new audience, details like Buffy and Drusilla's shared birthday keep even the most loyal fans coming back for more.