"So that's why..." Yuriko mumbled as she let her hands rest on her now-existent C-cup breasts. Normally flat-chested, the new breast flesh was completely alien to her skinny body, and even more so on her short stature.
It all made sense to her now why Chiharu was so incredibly large... and still growing! All that excessive and aggressive groping she'd been doing to her sister for the past two years, along with Densuke's accidental grabs here and there must be the reason for why she was so freakin' large!
Before testing again, she tentatively began to undo her bra through her shirt before fishing it out from the hemline (a skill she'd been practicing in order to try and win Densuke over), her new unsupported and unrestrained breasts stressing lightly against her small blouse, nipples pressing against the fabric in her excitement.
She let her hands rest on her newly acquired breasts before she began to press aggressively into them, pinching the nubs of her hardened nipples through the fabric, kneading them with the ferocity of a psychotic baker, her hands maneuvering, flesh seeping between her fingers. Yuriko's body began to shake lightly from slight pleasure as she did it, her eyes glued to her breasts as she waited for them to grow, her hands not stopping for any reason.
As she began to realize she was groping much more powerfully than she ever had towards her sister, she paused as a slight warmth began to spread through her breasts, her flesh pulsing with heat as they visibly began to swell between her idle fingers. But, as the growth started, she knew she couldn't stop. Not until they were huge.
"Mmm... Chiharu..." She thought lustfully about her sister's breasts, thinking about how big she was... and realizing she wanted more than that. The flesh was pushing her hands further away from her chest as they began to swell at quite a quick pace, passing D-cups within seconds and were now shooting through F, G, J, L.... Yurkio's eyes fluttered shut at the though of how large she was going to get as, from the feel, she noticed her breasts had swelled past her sister's size and were still growing! As she felt the lobes of her breasts reach towards her navel, the gigantic masses caught in her blouse started to pull the stitching apart, audible stretching as she continued to pinch her growing teats through the fabric, not wavering in her groping. Finally, the blouse's weak stitching at the side gave away, the back of the blouse ripping completely from her body and falling, while the front stayed to her breasts as Yurkio kept massaging her breasts, the large sacs now reaching towards her waist, it becoming increasingly difficult to reach and pinch her nipples as they surpassed any cup size she could imagine.
Finally, she began to slow her attack on her breasts as she found it was taking effort not only to pinch, but to stand... the weight was enormous, especially with no support. Lifting her hands slowly from her mounds, Yurkio's eyes opened slowly in rapture to the sight before her. Her breasts took up almost her entire downward field of vision, a canyon on full cleavage extending about fifteen inches from her body before parting, breast flesh still pushing a few more inches out from her body. She could hardly see her nipples, the hard tips pushing out three inches from the ends of her breasts, which has pushed themselves a foot out to either side of her lithe waist and a few inches below her panty line, making the squishy flesh quite visible from any angle. Her back strained to hold the weight as she slowly walked backwards and sat herself down on her bed, her breasts resting on her legs and spreading out on just barely touch the rough sheets of her bed, her breasts pulsing with pleasure at the feeling.
Yurkio's hands came up, trembling slightly in rapture at her size as she let them rest at the top of her gigantic mounds.
"A-a-amazing..." She couldn't figure out what to do now, but all she knew is that whatever caused this, had made her the happiest person alive. She pressed just lightly into the tops of her breasts and watched in complete focus as her entire breasts began to jiggle for as long as a few minutes, the pliant flesh sending waves of pleasure into her, her eyes rolling back slightly...