Forget demons and warlocks. In Buffy the Vampire Slayer's last Halloween episode, Buffy's kid sister Dawn faced real terror: her first kiss—with a bloodsucker, no less. Michelle Trachtenberg, who plays Dawn, denies she had any qualms—save one. "My only worry was 'Will I have enough breath mints?' We did the kissing scene all day long, and it was really fun."

Still, older costars are protective of the 16-year-old unattached actress. "I'm glad to tell her all about teenage boys and their behavior," says James Marsters, 39 (rogue vampire Spike). It was big sister Buffy—Sarah Michelle Gellar, 25—who helped the die-hard Buffy fan get cast as Dawn last season. "I pushed really hard for her," says Gellar, who had been her castmate on All My Children in the mid-'90s before Trachtenberg went off to star in 1996's Harriet the Spy.

Now living in L.A. with her sister Irene, 23, a talent agent, and her mom and manager, Lana, 47 (who divorced their father, Michael, 53, a phone installer, in 1999), Trachtenberg attends private school and has a tutor on-set. "While we're all eating cake, she has to take a trig test," says Gellar. "She handles it with ease." For which Trachtenberg credits the show. "Buffy is just a metaphor for life," says the actress. "We each have to slay demons—a new job, the first day at school." Even—mint, please—a first screen kiss.