If I found out my sister was a slut, I would have pulled her in the asshole, too. For these guys, getting their asses handed to them is commonplace. Although for the look, they break for a few minutes, but when a couple of drops of lube appear - they quickly sit down anally on the phallus. So this little sister is nice to feel like a courtesan, to show off all her skills in front of her brother, to let him cum in her ass. Every bitch dreams of being the best at it.
It's nice to have a queen on your dick. Not just in appearance, but in demeanor as well. Then you feel like a king yourself, who is the only one available to this lady! Maybe with loose ladies sex is more interesting, but sex with the queen is a much deeper experience!