Ty's womb had been filled with Eileen's thick ejaculate, and in turn the man had released an innumerable amount of his sperm inside her. The energized seed swam eagerly through the girl's body, moving instinctually despite being just minutes old, and her form just as naturally accommodating them as his original body had produced and released them.
Soon they reached the point deep inside Ty's reformed loins which they sought, and found what her body had produced in their stead once he became she- a big fertile ovum, eagerly awaiting their intrusion. They set about wearing away at its outer walls, each and every one seeking to form offspring. This whole process was decoupled from conscious concerns- all that mattered to these cells was reproductive instinct, the possibility of conception.
Sure enough, one soon reached inside Ty's egg and bore its way to the centre, fertilizing the egg and making it implant in the young woman's womb, kicking off the process that her lover's old body had partaken in a decade and a half prior.
Outside her body, the reality of all this slowly irised back in on Ty as she felt Eileen pull out of her and his thick cum drip from both her creampied pussy and his thick cock head. Between pants, she slowly said, "Y-you just bred me."
"I said I would," Eileen agreed, smiling teasingly.