Well nothing I would tell him I'm sorry for what happened to you and it's not your fault what you did to Cayde it was Raven controlling you and I will tell him that his sister is alive. However a lot of people don't realize when a guardian becomes a guardian they do not have any of their memories when they were alive it's going to be a weird experience for him more than it would be for us because when we became Guardians none of the people we knew were alive. When he came back the people who killed him are still around when he finds out what he actually did when he was alive it's going to psychologically wreck him. a lot of people don't realize after he thought his sister died he had so much anger and rage and The Last Wish raid boss she just made that anger and rage more stronger to control him. Example just like how a demon would take over someone's body similar to in Supernatural where the demon would use the person's emotions to control that person further to make The Possession last longer. Yes I know two different things a game and a TV show Supernatural but possession between those two aren't that different. It's funny how all the people who are commenting are saying the most stupidest stuff I have ever read on the internet.