Hi there,
Spoiler
Did you meet your vassal while exploring the void? In chapter 3 did you revisit their room to build their bond convos?
Each companion has 6 endings high stat + complete bond relationship ( mikail+power+romance ,mikail+power+friendship, ect ) when ilyon woke up did he reunite with mikail and survive noctisse? If not then you didn't do enough bond conversation with the companion in chapter 3 keep leveling up either their romance or friendship high enough and keep revisiting their room to unlock more convos.
Hope this helps but not entirely sure of the question tbh.