Kirito and Asuna are almost surely main characters in 'Sword Art Online Last Novel'. In addition, there may be other recurring characters like Klein, who has been Kirito's friend from the start. Sinon, who has her own story arc related to marksmanship in the virtual world, might also be an important part in the last novel, depending on how the story progresses and ties up loose ends.
The main characters are likely to be Kirito and Asuna. They have been central to the Sword Art Online series throughout, so it's expected that they play important roles in the last novel as well.
Chapter 273, ""Justice Will Eventually Triumph Over Evil", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. It opens with Jiang Li, who was reading a book, suddenly jumped in fright.
Chapter 292, "Coming and Going, Gathering and Parting, Human Nature", is the clearest early answer because it turns Going's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Li slowly lowered his hand.
Chapter 261, "They've Ruined the Entertainment Industry!", is the clearest early answer because it turns Shu Yan's situation into a concrete plot event. Early on, The village chief's eyes nearly popped out after he heard the whole.... By the end, Is it necessary to be so guarded against me?.
Chapter 237, "Top of the Three Lists! Truly Deserved!", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. A useful checkpoint is the way the scene starts with It seemed as if, believing the spilled water couldn't be recollected,...
Chapter 217, "No Problem, They're All Red Anyway", is the clearest early answer because it turns Director Sun's situation into a concrete plot event. The chapter turns that into something concrete by moving from But Director Sun didn't plan to give her any room to think, he...
Chapter 364, "This is the gift our master sends you for the first meeting", is the clearest early answer because it turns Jin Siyue's situation into a concrete plot event.
Chapter 164, "Congratulations to Jiang Yan for scoring one point!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Damn, the production team is so shady, they're still doing a live...
Chapter 243, "How Could It Be Her?!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. It opens with Hahaha, the young master's face has gone white, but I got a scare...
Chapter 276, "He Will Definitely Make This Woman Pay a Price!", is the clearest early answer because it turns Cai Shaoguang's situation into a concrete plot event. Early on, After listening to Jiang Li's words, Shen Lan's brow furrowed again..
Chapter 132, "Looking at me with that kind of eyes, are you afraid I'll eat you?", is the clearest early answer because it turns Brother Niu's situation into a concrete plot event. The chapter turns that into something concrete by moving from The new girl in the live-streaming room went crazy.