Felicia Day

It took eight seasons, but finally Felicia Day has come to Supernatural.

"It has always been one of those shows that I’ve wanted to be on," Day tells TVGuide.com. "I feel like having done Buffy [the Vampire Slayer so many years ago, this probably comes the closest and sort of has that vibe. Whenever I watch it, I think to myself, ’Why am I not on that show?’ It’s such a cool thing that they just called me up and thought I was perfect for the part."

From Game of Thrones to Downton Abbey: Check out Felicia Day’s watchlist now!

The uber fangirl favorite is one of many Whedonverse alums who’ve stopped by to help (or hinder) the Winchester Bros. On Friday’s episode (9/8c, The CW), Day plays Charlie, a computer-savvy tech working for Dick Roman (James Patrick Stuart), the billionaire whose body was taken over by the lead Leviathan. She runs into Sam and Dean (Jared Padalecki, Jensen Ackles) during their investigation.

"It’s a situation where they come to me when they learn that I have acces to a certain hard drive they need," Day says. "This is certainly a different world for her. She’s an IT employee at Richard Roman Enterprises, so this supernatural stuff is something she’s never seen in real life. But that’s what I like about her. Even though the situation seems overwhelming, she’s able to find that bravery inside that I don’t even know if she knows she had. Through the episode, it’s really interesting to see the arc of how they get to know each other."

Charlie isn’t just an IT employee and amateur computer hacker, however. She’s also a geek who shares many of the same interests as Day herself. "When I first read the character on the page, I was like, ’This is tailor-made for me!’ Charlie is a fangirl, so this was a meta moment. It was easy to picture her walking around the Comic-Con floor. In her cubicle and her life, she has a ton of awesome stuff, some of which I actually own as far as figurines and posters and comics that she likes. So it was almost like walking into my office when I was walking onto the set."

Case in point is the sword that we see Charlie brandishing when she meets Sam and Dean. It just so happens she owns this weapon, something the character shares with Day. " I do have some swords. In fact, I did a project last year, Dragon Age, in which I trained extensively using swords. I don’t know if Charlie’s taken sword classes, but owning a sword is one of her dreams as an adult. It’s a great scene."

That scene is typical of the quirky humor in the episode titled "The Girl With the Dungeons and Dragons Tattoo." "I don’t want spoil anything, but there is a reference to a tattoo that’s one of my favorite lines in the episode," says Day. "The writer of this episode is a geek at heart and obviously went to town on this character."