"I know what I wanna try now," Ty said as they broke off a kiss.
"Yeah?" smirked Eileen.
"Well, you seem to be having a lot of fun in the opposite sex's body," the boy smirked, pulling off his clothes to give her a show, "I wanna join in!" As soon as he had gotten naked, he focused on the wish: make myself a girl.
They both watched in amazement as Ty's body rapidly started to reshape itself, feminine hormones coursing through him. He could tell why Eileen had been so aroused when this happened to him: the feelings were amazing. He could feel himself physically shrink inwards, not merely slimming down but his muscles turning more lithe and his hands and feet more petite. Soft curves had formed around his body and his shoulders had shifted inwards. But there was a tensing elsewhere where something was starting to grow instead of shrink. He bit his lip and then let out a high-pitched moan as his nipples expanded and felt larger, puffier, more sensitive. Before his eyes his chest was swelling, large soft wobbly mounds forming on it, which he ached to have touched. He'd grown breasts.
Ty felt Eileen's hungry male eyes on him, and to his surprise it felt kinda nice. He felt deeply attracted to Eileen, and the confusion in his head had almost totally vanished. Peering past his new boobs, he saw the only part of his body that hadn't changed yet, and gasped as he felt it start to. His penis shrank away, the long shaft receding inch by inch, his scrotum flattened and his testicles moved up inside... her. By now Ty didn't feel like a boy anymore. As the lumps inside her pulled upwards they reshaped into her ovaries and connected to her womb. In the space between her legs formed vaginal lips and an opening, and what was by now a tiny nub finished its shrinkage and formed her clitoris.
She kissed Eileen passionately and felt her female juices moisten her new slit. As the handsome man's large dark penis rubbed against her she practically shivered with pleasure. By now, Ty and Eileen were practically beyond rational thought- the lustful haze of transformed arousal meant they were acting on biological imperatives. They wanted to mate, to breed, to pass on their genes.
Eileen carefully rolled Ty onto her back, and pushed his phallus inside her. He pounded the girl eagerly, loving how it felt to be male- the strength, the almost uncontrollable arousal, the knowledge he would make someone bear his young all felt intoxicating.
Likewise, Ty was transfixed by how it felt to be female- she loved the intense sensitiveness of her body, the way pleasure seemed to come from everywhere instead of just one part, and the knowledge she could be impregnated and bear young when she never could in her old body. She clung to Eileen, who felt huge both inside and above her, his bulk seeming extra arousing.
Their fucking was intense, Eileen's firm chest pressing against Ty's soft boobs and his balls slapping against her body, and it didn't take long for both of them to reach massive orgasms. Eileen groaned loudly and shook, his balls twitching as he shot several warm loads inside Ty's pussy. In response, Ty's body convulsed as she reached her first female orgasm, her walls clenching around Eileen's cock to milk him dry while her nipples and clitoris pulsed and she moaned and panted with pleasure.
They hugged each other tightly and kissed a little as they came down from the high, and reality slowly irised back in.