I wasn't strong enough
That was the last thought Castiel had before the Leviathans took over his vessel, and then, all he could think was-
trapped trapped pain weakness all my fault death destruction all my fault
-He could see everything, feel everything, hear everything, but it wasn't him. It was the Leviathans, and they laughed, as he screamed and fought to free himself from them-
let me out trapped let me out nonono all my fault
-And then, they walked into the water, and, in that split second before they dispersed, he knew their plan-
oh Father nonono all my fault
-But he couldn't stop them. He was too weak-
not strong enough broken broken trapped useless all my fault
-That was Castiel's last thought, before the Leviathans burst out of him-
ripping tearing pain oh Father make it stop stop please no all my fault
-And then Castiel knew no more.