She's bigger than him in at least one way

Valentino burst through his sister's door. "Lucia! It's okay, just calm down and be quiet, we don't want mom and dad to..."

He trailed off as he met Lucia's gaze, which was surprisingly not of panic or fear, but of lust and control. Then, his gaze dropped lower to the eight inch cock sitting in her hands. Lucia stretched herself out on her bed, lazily jacking her rod to full attention.

"Hello, brother dearest," she purred, crawling sensually towards him. "Do close the door and come closer."

Stiffly, Valentino did as he was told, and quietly shut door. He hesitantly sat down beside her. "Lucia. You're taking this... well."

She grinned. "I just feel so calm, like I was always meant to have this gorgeous beast. You should come closer, I'm sure you'll feel that way soon."

As she beckoned him closer, he could smell the potent musk wafting from her impressive dick. His head was starting to become fuzzy. All his troubles were melting away, leaving him with this soft serenity washing over him. Lucia gave him a smile.

"That's right, it feels so good, doesn't it? You know what, brother? How about you lose the pants. See how your rod compares to mine."

Valentin obligingly stripped off his pants, though he hesitated at pulling his underwear down and exposing his miniature dick. A harsh look from his sister, however banished all thoughts of resistance, and he quickly pulled down his boxers. Lucia threw back her head and laughed.

"I knew you were small, but that is just pitiful!" She flicked his tiny, two and a half inch diclet, sending a rush of hot pleasure through him. She scorned his display. "Is it that easy to bring you to the edge? You should be ashamed."

Valentino was. He looked up at her with round eyes. "Please don't punish me."

"You're lucky I'm so merciful," she hissed, grabbing his face and dragging it until it was a mere inch from hers. She licked her lips, her eyes darting around his face. "But I don't want you touching that thing again. Your hands are on me."

Valentino nodded, and brought them to her eight-inch erection. He slowly slid them up the shaft, slicking her rod with the copious amounts of pre-cum dribbling down from her swollen, angry head. Lucia shivered at the touch. "That's it, brother. That's what makes me more of a man than you. Do you like feeling it? Do you like knowing I am four times more adequate than you will ever be?"

"Y-yes, mistress," he muttered. His face was burning with shame and desire. He bowed his head. "You are worthy of worship. I am nothing."

"That's it," purred Lucia, stroking his hair. "I own you. Now, make me cum!"

Valentino's movements suddenly sped up, one hand frantically sliding up and down her slick shaft, the other cupping her egg-sized balls. Lucia moaned, arching her back and curling her toes as the pleasure of her first handjob hit her like a truck. Her cock somehow managed to become even harder, each vein throbbing in Valentino's hands as he threw everything into making his sister - his mistress - feel as good as possible. With every lust-filled groan, his jerking off grew more intense until finally, with a shout of pure ecstasy, he felt the first rope of cum burst from Lucia's cock.

He was drenched in white as his sister's dick painted him with her pungent seed. Panting, the pair collapsed and basked in the afterglow.