There was really no need to ask him to come, or express any will in that direction what so ever. At the moment, Cass was too far gone to have stopped himself even if he wanted to.
Moaning, his eyes fluttered closed and he let his head fall back as Percy took over. It only took a few touches, and he felt his body shake with the first waive of intense pleasure, only to feel waive after waive roll over him, making his entire body shudder as he came over Percy's hand and both their bodies, his come mingling with Percy's.
He didn't open his eyes until he a few moments after, but when he did, and saw Percy looking at him, he couldn't help but to smile. 'Come,' he murmured, pulling Percy's face close to his own as he kissed him again.