Nautilus isn't in pain, exactly, but it's close. It's incredible loneliness. He is isolated physically by his suit from others, he's isolated by his size, and he isolates himself because he no longer identifies with humans.
Varus also has exceptional pain. The only thing that still drives him is his pact with the... "thing" from the Pit of Pallas in order to avenge his family. Once he avenges them, he will have done what he wanted and he will be free to leave this life which will then hold nothing for him. Nothing to love any longer, and nothing to hate any longer. He has lost everything he knew and has given up everything he was for this.
Diana is very much in pain as well. She was betrayed by her people who ridiculed her and attempted to kill her for speaking out. Her story is about her abandoning the main path and walking the lonesome road because she truly believes in it. Did you listen to her login song? It's incredibly moving.