Castiel wasn't the most energetic man. He was quite the opposite.

Even though he was an Angel, and he didn't need sleep, he was always pretty exhausted, emotionally at least. He was stoic, and a bit quiet sometimes, and what Dean would call a ‘grump’.

You, however, were the opposite. You were bubbly and energetic, talkative and happy-go-lucky. It made you a pretty likable person.

Despite how ‘grumpy’ Dean claimed Castiel was, he always had a soft side for you. He wouldn't tell anyone, but you were his favorite.

He hung around you a lot. It didn't take too much energy, because if you noticed Cas was too tired to talk, you would talk enough for the both of them. Or just be there for him physically, if he was too tired to listen. Most of the time he listened though.

It was an unlikely duo, but it worked.