It doesn't matter that Midoriya is corrupted. Kaworu still sees him as the boy in his memories from their last happy days of flying kites on the beach, all flushed cheeks and big smiles. That's who he is on the inside.

As for himself...

"I've killed more people than just those. And I hurt more people when I was a beast. I think I hurt Shinji-kun back home. Can you really care for something like me? Or is what you feel actually pity?"