She's an assistant teacher, so she helps teach

Your dick is deep in Mallory's trembling throat, so you don't feel any particular need to interject. You push the head in your lap down against your crotch and watch the fit little island babe explain herself.

"Actually, I guess so. I was just saying that sucking dick like these students over here is a great warmup for a rookie diver."

Doug's stern face lightens a little. "That's right, and it's great for getting the blood flowing in the recipient diver too. Why don't you demonstrate by sucking my dick while I continue the lesson, Kira?"

Kira sighs and looks at the floor before shrugging and saying, "okay." She walks down the aisle of the bus and kneels in front of Doug.

"Not like that, Kira. Lie down on the seat, with your head in the aisle."

The pretty diver sighs again and climbs onto the seat next to Doug, lies down on her back, and hangs her head off the seat into the aisle. As Doug unzips his wetsuit, preparing to fuck her pretty face, she turns her head to the back of the bus, looking up at you pitifully for just a moment.

The sight of Kira on her back for Doug, but silently begging you from down the aisle is enough to make you cum in Mallory's throat. You pump load after load of your jizz into the pretty face in your lap, and then the bus driver calls out, "half way there, folks!" Doug, meanwhile, has is holding his dick over Kira's mouth while she bites her lip.

Just as his cock is about enter Kira's lips, Doug spins suddenly around, a shrill whistle shrieking from the air tank on his back. He plants himself on the seat across from Kira and begins removing his gear. Kira, still lying on her back, quickly puts away the diver's knife she had slipped into her hand, and turns again to you with her beautiful, imploring face. Regardless of whether you're too dumb to realize she has sabotaged Doug's scuba gear, you're still horny enough to recognize the look of a girl who wants your dick in her face.

You shove Mallory aside and bound down the bus aisle to the seat where Kira is lying on her back. You plop your semi-hard dick on her face, balls on her forehead, little wisps of aftercum from your previous blowjob trailing across her upside-down face. Then you slide into her mouth, folding her tongue back and forcing yourself deep into her throat. You ram her horizontal windpipe with the full **** of your practiced pelvis, and she flails around until grabbing at your butt to hold still.

The driver keeps eyeing you in the rear-view mirror, but the ride is smooth, and you enjoy enough stability to really slam your dick into Kira for the remaining miles. Doug is going over some scuba tips with the rest of the class while you fill his assistant teacher's throat with your cock.

When he cautions the noobies against holding their breath under the water, due to the dangers of pressure changes, however, you decide to pinch poor Kira's nostrils shut and demonstrate the contrasting lack of danger when sucking a dick. As soon as you block her airways, she begins to thrash and flail, eyes wide with fear, but of course she's actually fine. You hold her nose tighter, and shove your cock deeper, and she begins slapping your ass, clawing at your stomach, and imploring you again with her pretty brown eyes, only this time not begging for your dick, but your mercy.

Of course you have no mercy, and you keep her throat plugged tight as you pump her upside-down face harder and harder. Finally, after a minute or two of flailing, she stops, realizing she should have suffocated by now, but hasn't. Just a few seconds later, she is back to the same relaxed pose she had when you started, her eyes a little red and watery, but not so terrified anymore.

As the bus pulls into the dive site's parking, you hear Doug explaining that a blowjob is the only other way to safely go underwater for extended periods, so if anyone's gear malfunctions, or if they're just looking for a thrill, they should try 'dick breathing' like Kira here is demonstrating. You look down the bus' aisle and see all the scuba student babes watching you intently, considering how they might use your cock for a life-saving device, or simply for their entertainment, and you pull out and cum all over Kira's beautiful face, dripping some gunk in her pretty black hair.

"Mmmm, thanks David. Always nice to work on advanced techniques," she says, wiping the jizz from her forehead.

"Alright, everyone off the bus and suit up!" Doug ushers the girls, and you, off the bus, and towards the water. "Find your dive buddy and get ready!"

"What's a dive buddy?" You ask Kira, not knowing anything about anything, but also not knowing anything about scuba.

Kira, happy to explain though still catching her breath, says, "you always have a buddy when you're diving, so if anything goes wrong, someone is watching you and ready to help out. Do you not have a buddy?"

You look over the group of students, and pick the hottest one to be your buddy.