The series, which will arrive as part of DC Comics' second wave of New 52 titles in May, will focus on the arrival of Earth 2 residents Power Girl and Huntress on the main DCU Earth.
Levitz told Comic Book Resources that "these two gals who are 16, 17 years old, something like that, when they cross over", meaning they have been lost in reality for about five years in the current time frame.
"Well, a lot of things happened in those years," Levitz continued.
"We don't get to find out all of them immediately, but one of the fun things that we're doing is, the sections of the story that Kevin Maguire is drawing for the first four issues are all set in that period, picking up from the moment they arrived on the Earth to showing little bits and pieces of how they got to where they are now."
The Legion of Super-Heroes writer outlined the differences between the two characters.
"Helena's definitely more tightly wound," he said. "She's focused herself in on how she's going to make this world her home, the difference she's going to make here.
"Kara has resolved to get back where she came from. She thinks that's the most important thing she can do in life, and there's got to be a way to pull it off. She's clearly a more confident person, being used to being invulnerable and, really, one of the small handful of the most powerful beings on the world she came from.
"She comes in with a very different approach to the world, but that doesn't necessarily serve her well on this Earth, which has a different set of everything, from laws of physics and nature to a very different set of inhabitants."
DC previously released the designs for Huntress/Helena Wayne as Robin and Power Girl/Kara Zor-L as Supergirl on Earth 2.
Worlds' Finest #1 will debut on May 2.
Photo gallery - Worlds' Finest covers: