Young girls sucking to please guys and keep them around. Nipples are successful and attract males. Everyone wants not only to fuck her pussy, but to give her in the mouth and cum after that. It's a pleasant sight - the partner's lips smeared with cum, the drops dripping from the end on her tongue, her breasts smelling of sex. For a man, this picture is the height of bliss. With that, the girl is down, expressing submission and acknowledging his power over her.
What else are sisters for? They're just for my brother to practice on her, to relieve his tension. Then he could achieve something in life instead of hanging out in dubious companies. And the sister won't be shortchanged.