Personal Upgrades

You open a new profile in the app, entering your own name, John.

A profile of yourself appears, naked and showing all the faults you've hidden, lied to yourself about, or in a few occasions tried to correct.

Extra weight, undeveloped muscles, and of course your entirely average genitalia.
Penis 5.5 inches long when hard, and of average girth.
Testicles an entirely average or possibly small example in the average range. Perfectly serviceable for the average female's needs and desires, but for your girlfriend it will never be enough.

Well that's changing first.

You dive into the menus, expanding subsections and exploring the details.

Eventually you arrive on the changes you think will serve best.

Your dick will be a thick and girthy 6 inches long when soft, with weighty balls at the size of small oranges. They will expand with time since last orgasm, or with sufficient stimulation of the sexual variety, reaching a maximum size approaching large oranges or small grapefruit. Output depends on stimulation and some other factors, but you leave it more or less at "normal" (at least for testicles that large). You do up your cum production rate to keep things ready to go fairly often, but get distracted by the cock size options.

When aroused your cock will now grow to no less than 7.5 inches in length, and add another half inch to it's girth, but the key part you had to dig through half a dozen nested menus for is the "Perfect Match" option. This shit has to be magic, or else technology is way beyond what you thought, because it promises your dick will grow bigger until it's the perfect size for whoever you're about to fuck. It only let you set a lower limit, so you make a mental note to never try and seduce any elephants or whales.

But your girlfriend should be quite pleased, at least in that department.

You consider giving yourself the body of a fitness model, but decide that would be hard to explain.

Instead, you dig through yet more options and end up with what claims to be "Sexual Exercise Mastery", wherein you can set an ideal body appearance and achieve it by simply masturbating (although that's far slower) or fucking.
Apparently it will increase the calories burned by those activities to an **** level, at least until you reach the ideal body type, and claims you'll end up with monstrous sexual stamina as well.

You search through the menus and end up with a fit but not cut body target, lean muscles and a hint of abs, but with those muscles being far more effective than they appear, and combined with a stamina boost to insane levels, especially if engaged in sexual activities. If this app isn't lying, you'll only need to consume the necessary fluids and fuel to keep fucking for literal days without a pause.

Maybe you went overboard, but your cock thinks it's a good idea, straining against your pants as your fantasies of debauchery expand to include multiple partners.

You should listen to your cock, it knows what is best.

Based on the numbers, it would take you a few months of constant masturbation to reach this target, but if you can manage to get your girlfriend in the metaphorical sack, it will only take a month or possibly weeks.

Feeling a bit daring, you hit the necessary buttons to apply the changes, and feel your already hard cock grow to a hefty 10 inches long, extremely uncomfortable as it is crushed against your much larger testicles by your pants.

Pants you quickly remove, staring down at the monster you've conjured. Or this app conjured?
Apparently this is what you think the perfect size for masturbation is?

Hell yes it is, who are you kidding.

You swipe back to your girlfriend's profile and stare at her newly huge ass as you start masturbating.
Fantasies of her bouncing on your cock and taking a massive load up her ass fill your head as you quickly approach climax.