[If he had never met Yu Kanda, he probably would still be somewhere not worrying. Now he has to worry. Yu Kanda has to save the world from the Apocalypse and he can't do that if he's incapacitated in any way.]
Castiel. We were sent to bring you from Hell and we've been assigned to assist you in stopping the demon, Lilith.
[Perhaps Yu has chosen to block out recent memories in order to protect himself from the horrors of Hell.]