From KI we know that Pit is the captain of Palutena's guard, from her prison in Skyworld she sent a bow to Pit in his prison in the Undeworld. Pit uses this bow to shoot at enemies and goes on a quest to find the 3 Sacred Treasures: the Mirror Shield, the Wings of Pegasus and the Arrows of Light so that he can slay Medusa with them and save the day. along the way he can free Centurions turned to stone that later come to help him in boss battles.
The 3 sacred treasures come back as his B moves and his Final Smash summons Centurions. that's good and all, but what about everything else?
what about this cut scene www.youtube.com/watch?v=NQ1JFa… this didn't happen "like this" in KI so we assume this is just Brawl's interpretation of what Pit's life is like. But the similarities don't match KI the way they match KIU