Chapter 1 is basically getting to know my version of the KI:U cast, with Pit slowly going mad that he sees his "Dark Truth" in any mirror, despite Dark Pit being his own being(we learn that it's his Dark Desire later on in the story).
Chapter 2 is getting to know the Heavenly Virtues, and how they try to help Pit with his situation, and learn on how they knew about Pit despite him not knowing them(or remembering them..) and their interactions with him and the rest of the crew
Chapter 3. Shit. Hits. The. Fan.
that's it.