Jeff and Sarah stood in front of the mirror, with milk leaking into their bras. Jeff was groping himself, still not used to his new chest. Sarah was getting aroused at the sight of her boyfriend with such a beautiful rack; she began to rub her pussy through her panties.
'Jeff, can we... Feed your sister?' Sarah said, hesitantly. Jeff looked at her, a big grin plastered on his face.
'I love you, babe,' Jeff said, kissing his girlfriend as their leaky breasts pressed together, leaving a puddle of milk on the floor.
They went to the Chronivac, making it so Natalie loved breast milk as much as they did, although they didn't make her lactate; they wanted her dependent on their milk. They ticked the box labelled 'mental change', making it so Natalie believed it was normal for her to drink from her brother and his girlfriend's tits. They hit apply.
Nothing visibly changed around them. Jeff decided to take the risk and walk into his sister's room. He walked through the door, finding Natalie still asleep. He took his bra off, letting it drop to the floor, and went to Natalie's side. He shook her awake, his large breasts hanging in front of her face.
'Hey sis, feeding time,' he said. Natalie rubbed her eyes, and upon seeing her brother's milky breasts, pressed her mouth to his teat. She sucked hard, licking his nipple, filling her mouth with her brother's breast milk. She closed her eyes in satisfaction as Jeff pushed his chest out, moaning lightly. She took her mouth off him for a second.
'Where's Sarah?' Natalie asked. Sarah walked into the room.
'Here, sweetie,' she said. Natalie put her nipple in her mouth too, hungrily sucking on both of their breasts. Jeff and Sarah were in bliss, watching this beautiful girl suck on their teats. Jeff put his hands down his pants, and began to stroke his cock. He took off his pants, exposing his penis to his sister.
'If you want any more,' he said, taking his breast out of her mouth, 'you gotta do me a favor first.' Natalie obliged, as she took his cock into her mouth, starting to suck just as she sucked on his nipples. Sarah looked at the sight of a girl sucking off her own brother, making her aroused as she rubbed her pussy through her panties.
Eventually, Jeff came into his sister's mouth. Natalie wasted no time, going from Jeff's cock straight back to their nipples, filling her mouth with a mixture of cum and milk. Jeff and Sarah loved the feeling of Natalie on their tits, as they both moaned.
Jeff and Sarah kissed, Natalie still sucking their breasts, as they thought about how they could take their new fetish further.