The content, set before the events of The Last of Us and representing the first single-player expansion that developer Naughty Dog has ever created, will introduce players to the "real" Ellie and focus on her interactions with her friend Riley, Johnson said.
"You'll definitely see a more playful side to Ellie and get to know her a bit better," she said. "You're going to see a lot of different sides to the character that you definitely didn't see in The Last of Us."
Regarding how Left Behind "feels" compared to the main campaign, Johnson said you should absolutely expect something different.
"It's a little bit more 'fun,' because you have two teenage girls going through a mall. It's kind of like a post-pandemic version of two teenage girls hanging out. Definitely not a normal hangout! It's very different--a little more playful."
Players will engage in combat that feels familiar to the original Last of Us campaign, but Johnson made clear that there are "some new touches and nuances, too."
Johnson wasn't ready to spill all the secrets about Left Behind though, as she would not confirm if players will get to learn more about when Ellie is bitten by one of the infected, which she mentions during the main campaign while with Riley.
"Playful" appears to be the tone Naughty Dog and Sony are going for with The Last of Us' Left Behind expansion, as Riley voice actor Yaani King also used that word to describe the game.
"You're going to have a little more fun, I would say," King said in an interview with IGN. "One thing I can talk about is what you kind of see in the teaser trailer, the carousel scene… you get to be a little more playful, you get to see a side of Ellie, along with Riley, that is a bit more carefree, not so focused on the world that they live in and the reality in which they live in, but you get to explore a playful side of Ellie that you don't necessarily get to see. And you get to see her through Riley, who's kind of bringing these things out of her and loosening [her] up a bit."
Left Behind launches exclusively for PlayStation 3 in early 2014. It is included with the $20 The Last of Us DLC season pass and can purchased separately. The Last of Us was one of the few titles Sony demonstrated last week at CES 2014 running on the company's new PlayStation Now streaming service, which goes into beta later this month.