I don't know for sure as it's a fanfic. It could have Naruto and Sasuke from Naruto, and perhaps Edward or Bella from Twilight if it's following a more traditional combination of characters from both series.
Since it's a fan - made work, the main characters could be entirely new characters created by the author. However, if it adheres to the general idea of combining Naruto and Twilight, we might expect to see Naruto as a central figure. He could be on a quest related to the 'twilight key'. And maybe he teams up with a Twilight character like Alice, who has the ability to see the future. They could be the main characters trying to figure out the mystery of the key and how it affects both their worlds.
The main characters could also be secondary characters from both universes that are given a more prominent role in this fanfic. For example, Shikamaru from Naruto could be a key player. He's known for his intelligence, and in this fanfic, he might be the one to figure out the true nature of the 'twilight key'. From Twilight, Jacob could be involved. He's strong and has his own set of powers. The two of them might be at odds or working together in relation to the key and the events it sets in motion.
Chapter 235, "Bungee Jumping in Ethiopia???", is the clearest early answer because it turns Yang Ren's situation into a concrete plot event.
Chapter 296, "It's Over, I've Kicked the Iron Plate!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from This grand fan meeting soon caught the attention of the entire...
Chapter 286, "I Won't Let Anything Happen to Either of Us", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with Throughout these reincarnations, Zhao Lang had gradually discerned a...
Chapter 350, "Methods to Improve the Peak of Cold Resistance, Moao's 10th Town, Beishuo Yang Fa, Nightmare, Lu Yun of East Ridge", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. Early on, Hmph, the Nine Towns have had an agreement long ago: if a Xianyang.... By the end, Evidently, the other party didn't believe his self-introduction just....
Chapter 177, "You Annoy Me Just By Being Here", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter gives readers a real answer by opening on I'm actually the last?!" After the scores were announced, Wen...
Chapter 46, "Why Am I Second to Last?!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 154, "He Came, Bringing with Him the Bastard Game", is the clearest early answer because it turns Ahhhh's situation into a concrete plot event. The chapter turns that into something concrete by moving from Hahaha, I'm dying of laughter, Lili, do you really have to be so...
Chapter 340, "Seclusion, Growth of the Yu Generation, Family Banquet, Rapid Development (Part 3)", is the clearest early answer because it turns Xia Yuyao's situation into a concrete plot event. The setup is Dad..." "Dad..." The two little ones, no longer restricted,..., but the pressure keeps building through Of course, because their walking was still unsteady, it was more of a....
Chapter 424, "He Must Be Very Strong", is the clearest early answer because it turns Team's situation into a concrete plot event. The chapter gives readers a real answer by opening on Shh!" Jiang Yan, who was leading the group, turned around and made a...
Chapter 258, "Explosive! Jiang Li and Director Sun Are Having an Affair!", is the clearest early answer because it turns Director Sun's situation into a concrete plot event.