Now's as good a time as any

Smirking, you reach down and unzip your pants, then pull down your boxers. revealing six inches of still-flaccid cock.

"Christ, it's as big soft as most men are hard," Ava says, sliding off the bench and onto her knees in the grass. Her hands -- it took both of them to fully heft your cock's weight -- quickly worked to get you back up to full erection.

Within a minute, the towering pillar that was your penis is back, all foot-plus of it. Ava pulls her shirt over her head and shuffles forward, wrapping her massive tits around it. "Wow, it's bigger than my cleavage!" She says, the head easily clearing the tops of her breasts.

"Biggest cock on campus, probably," you boast.

"No 'probably' about it," Ava says, in between attempts to wrap her lips around the head. "This thing is a monster."

Your pre-cum has rapidly added to the lubrication of Ava's cleavage, so she begins to work her way up and down your pole, using her elbows to increase the pressure her huge tits can bring to bear. You groan in pleasure. It's not as good as her pussy feels -- nothing could ever be that tight -- but it's pretty excellent.

"Go ahead and come alllll over your girlfriend's big tits," Ava says, looking up at you. "I'm going to parade around campus with your cum staining my top, to show just how much of a stud my boyfriend is."

That's enough of a tease to push you over the edge. With nary a word of warning, you feel your climax start to build, and then--

The gray silence falls over you.

You, Her, or Bank?

Bank, you think without hesitation.

The world snaps back into color and motion, and your first cumshot comes rocketing out of your dick, up and over Ava's head and splatting wetly on the sidewalk behind her.

"Holy--" Ava says, caught off-guard, and without even thinking about it, lunges forward to wrap her lips around your cock. "Mmmph!" Her cheeks puff out as shot after shot unleashes into her mouth, rapidly starting to leak out of her imperfect seal and down onto your shaft and the tops of her tits.

Six, seven, eight -- each huge shot feels like it would be enough to fill a shot glass. Your balls must work overtime to generate this much cum, you think, as your ejaculation finally begins to tail off.

Ava slides back off your cock, and you watch as she takes a huge gulp, the bulge of your cum practically stretching out her throat as it goes down. Despite her belated efforts to contain your cum, plenty frosts the tops of her breasts as well.

"Damn, you really do come like a firehouse now," she says, licking her lips and pulling her shirt back over her head, the cum immediately darkening her top in big, wet blotches.

"Thank you," you say, somewhat lamely. "Oh, right! I, uh, banked the change this time."

Ava looks up at you curiously. "And?"

"Nothing has changed about either of us, as far as I can tell," you say, stuffing your softening penis into your pants again. You quiet your mind to see if there's anything else you can think of that might have changed, and discover...

"I... 'know' that I have a change stored up. It's... it's like it's right beneath the surface, and I could just let it take effect at any time, on anyone I wanted."

"Sweet! That means we don't need to worry about having too much sex, since you can just bank away the changes instead of having to keep applying them to both of us all the time!"

"I think so, yeah." There's definitely a little... pressure? to use the change that you can feel. Hopefully that doesn't build up too badly over time, or you're going to be firing off changes like a malfunctioning genie.