Knives is outside of the cabin, actually. He is installing some technology to the roof as Vash comes inside. He has set up a communication relay to allow the cabin to get in contact with his people quickly.

He's taken off the jacket he usually wears, so as he works he has on just a tank top with his muscular but pale arms exposed to the air. When Vash approaches, he turns a bit to look at his brother, taking stock of the boys and his twin.