As the bus' doors opened in front of the school and everybody got down, Erika's panties were still slowly stretching over her growing package. It was getting more plump by the minute. "I need to find everyone, tell them about the situation so we can make a plan before anybody gets found out..." Erika thought as she increased her pace.
As she came close to the building's entrance, her canine sense of smell caught a whiff of her friends; it was definitively Riley and Piper's scent! The two were often found together. Erika remembered the night at the sleepover, after they were exposed to the vial, when she saw the two of them kissing and squirming together in the dark. The memory made her bulge swell again, her furry balls threatening to slip out of her panties.
Almost running at this point, Erika followed the trail along the school's exterior, nose in the air, picking up the direction from which she could smell her friends. Turning around the corner, the scent intensified, and she knew she was drawing close. She unconsciously slowed her pace and changed her gait, her predator instincts taking over as she stealthily crept against the building's wall towards the back.
She peeked over the next corner, and spotted Riley and Piper in an alcove in the back of the main school building, gropping each other frantically. The wind blew more of their scent in Erika's direction and it hit her nostril clear as day: both of them were in heat. Her shealth thickened and throbbed once almost painfully, making her grunt under her breath. She tried to ignore it and watched her friends intently.
Both of them had opened their buttoned shirts and were caressing each other, panting and giggling. They had clearly gained over a cup in size, not quite yet C; more interestingly though, Erika's eyes trailed down and she noticed the additional pairs of dark nipples over their bellies, similar to a dog's teats but somehow more human-like. "So, the vial has the same animalistic effect as the salve but with an opposite gender..." Erika concluded.
Riley and Piper reluctantly calmed themselves, and Erika tried to listen in on their conversation. Her canine hearing picked up Piper's low voice: "... I'll head to the bathroom now, catch you later?". Riley nodded as she readjusted her skirt, and Piper buttonned her shirt before disappearing into the building through the nearest back door.
Erika was already typing a message to Emily on her phone: "Emily, quick: bathrooms before the Building A's back entrance. Catch Piper there, tell her to come to my house after school. You're coming too. I'll explain."
She put her phone back into her bag and sneaked upon Riley.
"Hey," Erika said in a husky voice, closing on the distance and appearing in front of Riley. "I saw you with Piper there..." Riley shuddered and turned around, unvoluntarily flashing her breasts and canine nipples to Erika. Erika looked at the teats and up again, her shaft stirring under her skirt.
"Oh fuck! Erika... I can explain! I..." Riley panicked, her back to the wall as her hands trembled, unable to quickly button up her shirt.
"It's okay Riley, I know everything. I know what happened when we slept at Melissa's house..." Erika went on.
"Please don't tell anyone about Piper and me! And this..." she gestured at her body. "I don't know what's happening to us, we just can't help it!"
Erika drew even closer, almost pressing Riley against the wall at this point. Now she was this close, she could smell all the details of Riley's scent, and almost hear her heartbeat. There was an aura of fear emanating from her skin, but also a radiating sexual heat coming off from under her school skirt. Erika could tell Riley was wet.
"I know, everybody at Melissa's sleepover was affected in a way or another. We can deal with this together, if you come at my house after school. There's ways to help... with this..." Erika said in a low voice, putting a hand on Riley's hip, narrowly avoiding her groin. She needed to be convincing.
Riley squirmed under Erika's hand, not knowing what to do. She felt strange, not just horny but there was a strange attraction to Erika; something about her scent. It was just so... comforting, and commanding. She felt weak on her knees, she wanted to be touched, she wanted to tear her clothes appart.
Erika breathed in another whiff of Riley's own intoxicating scent, imperceptibly closing on the small space between them, the fabric of their skirts meeting each other's. She just couldn't help herself in that moment, and she tilted her head up towards Riley's taller frame and licked her neck, tasting the sweat of her skin.
Riley was unable and at this point unwilling to move, and she arched her back so that her hips met with Erika's. But instead, her groin brushed against Erika's growing shaft through the skirts, and Riley heard a moan escape her own mouth. Erika's hips unvoluntarily bucked forward, pressing Riley against the wall as they grinded against each other.
Under the skirt, Erika's panties cracked, and a wet rocket lifted itself and both skirts, rubbing inside Riley's pressed thighs.
"Erika..." she moaned, unable to think of what to say. She wasn't sure what was happening other that it felt good and she wanted more. Erika hesitated for a second, before her instincts overpowered her once again.
"There's only one way to make the Need stop", Erika almost growled in her lust, her swelling cock rubbing against Riley's wet panties.
"Please Erika..." Riley begged.
She took Erika's hands and hurriedly pulled her to a nearby picnic table. Turning around, she pulled down on her panties and she sat on the edge at one end, lifting her skirt as she exposed her pussy with her thighs spread, oblivious to her surroundings. Nobody was around anyway, and few windows faced that side of the building.
Erika slowly moved to the table, pressing herself between Riley's legs with a hand under her own skirt as she took her hidden canine cock and guided it. Riley felt the wet tip rub against her clit, making her whimper in need. She couldn't see what Erika was doing but it felt insanely good. Erika directed the pointy tip towards the entrance and pushed in. Riley's lubricated hole swallowed her in once go, and they moaned in unison.
Erika's cock filled and stretched Riley's sex as her knot swelled rapidly, locking them together. Riley's hymen tore as the thickness increased, but she was too lost in ecstasy to feel it. Erika felt the resistance as she pulled back a bit, before slamming back deep into Riley, who leaned back on the table, to Erika's mercy. "That's it," Erika thought, "there's no going back. But we will both feel better after. Fuck, this feels so goooood...". She was growing back to her full length; the plump furry orbs swung heavily between her leg.
Riley bit her lips to muffle her lewd whimpers, her shirt open as she lay on the table, her hands grabbing at her own breasts and wandering over her canine teats. She didn't mind them so much; in fact right now she felt good about them. Erika looked at Riley's lithe body, the six areolas exposed to the fresh morning air, the human pair of breasts jiggling in rythm with her motions. The churning increased in her canine ballsack and she knew she wouldn't last much longer.
Increasing the pace, Erika slammed harder into Riley, going from deep to deeper since she couldn't slid outside anymore. It was difficult imagining how she could fit entierely, but perhaps the vial changed the female bodies that way. Riley was lost in the feeling of the dick inside her, which rubbing and swelling made her clench around and writhe in pleasure. She felt herself drawing closer to climax.
"F... faster, please! Please, Erika..." she begged again, the words leaving her mouth before she realized.
Erika's hard cock throbbed in Riley and her balls drew closer to her body. She let out a low grunt when climax hit her, a heavy surge of doggy seed escaping her to explode in Riley's belly. Riley whimpered lewdly as she came on the spot, arching her back on the table as their hips bucked together. Erika's cock kept spasming and throbbing as more cum filled Riley entierely, even backfiring out and dripping between them.
As they both calmed down and took their breathe, Erika's member softened enough that she popped out. They each pulled on their skirts to cover themselves, suddendly feeling self-conscious and vulnerable. Riley looked around in anguish, but there was nobody in sight.
"I... I should probably go," she said as she weakly hopped off the table and stumbled towards the door.
"After class. My home." Erika said firmly in her alpha husky voice. Riley felt naturally compelled to nod, before getting through the door and disappearing in the building's corridor.
Erika took a big inspiration, contemplating what had just happened. More complications, although now Riley had all the more reasons to work together.
As she took a step to follow after Riley, Erika felt dizzy. She staggered to the door and entered the building before falling to her knees in the empty corridor. There was a buzzing in her head, and her heartbeat pounded loudly in her ears. Her whole body shivered and trembled, and she felt her shirt stretch over her shoulders.
"Fuck... ghh..." Erika growled in a decidely masculine voice, this time. She looked down at herself and saw her hands become slightly larger, her arms and whole body became a little more toned, and her chest deflated entierely, leaving her bra empty. Her skirt felt as if it was a little shorter, and underneath her ballsack grew larger, her shaft thicker.
As with each time she had impregnated someone, her body was turning more masculine. This time, she had become fully male, though her hairstyle remained the same. The elastic of her bras snapped as her more muscled chest broadened, and she hurriedly removed it and her shirt. She saw the line of fur from between her legs creep over her belly, this time just past her navel. She put on her shirt again to hide herself, though her shoulders barely fit anymore. Her shoes felt uncomfortably tight.