She obeys, eventually

Julia did not move for several seconds. Unexpectedly the seat of the bike began vibrating strongly. Her eyes shot open and she grabbed the handlebars hard in shock. The blonde woman looked at her again.

Get off the bike and take off your pants right away - then get right back on. If you don't do this, you're going to cum right here in your pants. Don't worry, no one will find anything you're doing strange.

Julia hopped off the bike and pulled off her grey yoga pants revealing a saturated pale yellow thong. She looked back at the bike and found the seat had changed. It now included a 6" dildo as part of it. She straddled the seat apprehensively.

Julia started peddling the bike again, the floppy dildo slapped against her thighs. I want you to stick that cock in your wet twat Julia, the foreign voice buzzed her head. She tried to ignore it. Fine, have it your way.

The dildo became rigid and pressed against her thong. Julia tried to stand up a little straighter. The dildo grew, pressed more firmly against her, then started vibrating. Julia couldn't restrain herself anymore, she pulled her thong to the side and allowed the dildo inside her.

That's better. Now look at the control panel you'll see some new buttons. Enjoy yourself.

Julia glanced down, in addition to the normal display for heart rate and distance traveled there were new controls. There were up & down buttons labelled length, girth, vibrate along with an unlabelled dial.