So you want to write a chastity story? Perfect! Here is a little step-by-step on how to do it. Don't worry, it's easy! The majority of the stories all follow the same tried and true methods! Let's begin!
Step One: The before story flair. You can choose to include this or not. Basically, you made a statement beforehand stating it's a work of fiction and that if you don't like this kink don't read. Everyone will ignore this and will still proceed to read even if they dislike it.
Step Two: The Characters.
Characters are the easy part, you have your Main cast and you can have a few support characters. Don't worry about characterization or growth this is a website for porn we aren't here for that. Instead, insert paragraphs of Wattpad-like descriptions of your characters and what they wear at all times. ESPECIALLY the female characters.
Now a lot of stories follow along the POV of the one wearing the chastity device (Cock Cage or Belt depending on the wearer's genitalia)
If your character is a male, make sure he is completely stripped of all agency, he can't have any say in anything it doesn't matter what the dynamics of the relationship is (We'll get to proper BDSM dynamics later). If he does have a say, it's a non-choice or it's forced. Remember consent doesn't matter if you're a man. The male character no matter his physique or mental capacity is entirely trapped and unable to escape even the most basic of cock cages. (We'll discuss the merits of 'realism' in a fictitious story later)
Also, remember no matter the gender of your 'sub/slave' they are completely without support. They have no friends or family they can contact, and all services of combating abusive relationships ie (Police, International Domestic Violence Hotline, and other local programs) are completely ignored. They will at all times feel too 'embarrassed' or 'shamed' to ask for help no matter how much abuse they put up with. (This too will be covered in realism)
Now, remember your male sub/slave has no free will or choice in anything. The moment the cage goes on he's an immediate slave. He will do any and all things the 'Dom' or 'Mistress' tells him because he's just that desperate. He will immediately be perfectly fine with his long-time partner cheating and he will immediately cave and accept any and all sexual requests/demands. Never pay attention to his mental or physical health, just assume he can take it and go from there.
Now, for the female belt wearers. These are rare and not written about as much but there is still plenty of examples. You can apply everything from the male to the female belt wearer. She too will have no say or agency, will feel too meek or embarrassed to ask for help, and will do as asked. Her physical and mental health will constantly be taken for granted and she will have no support either.
No matter the gender just remember they are now objects not people.
Step Three: The Doms/Mistress/Mam's/Sir's Basically the person in charge of the relationship. Don't bother writing a backstory to them, don't bother giving them humanizing or redeeming qualities. They are entirely one-note and shallow. To put it shortly make them royal assholes that you just want to take a gun to the head. They are condescending, abusive, manipulative, gaslighting, and don't believe in 'Safewords' at a BDSM club these people would be banned for life but in fiction, they are praised and people 'wish' their dom could be like that.
The female version will always be hot and or sexy, and impossible to say no to. She will talk down or over her sub will convince the sub everything is entirely their idea and she's just 'being a good sport for going along with it' bonus points if she's the wife or girlfriend of the relationship that had been vanilla but after a month of being in charge, she decides she 'likes' this lifestyle too much and becomes the ultimate form of a dominating cunt.
It doesn't matter if she originally wasn't into any of this before but the moment she experiences the taste of power it immediately corrupts her. She will begin cheating and chucking her husband/boyfriend she will deny and tease to the extreme. Go back on promises or change her mind on a whim. She will demean and demoralize and be the exact opposite of a 'loving wife'.
The male Dom will be the same as the female-only he will most likely be a lot more violent and physically abusive, but that's okay cause he's a 6' 2" hot lawyer or Corporate CEO who's rich so it's totally fine. He too will demean and tease and just be an insufferable prick who will have multiple side pieces that he will engage with.
Just remember make you're Dom the villain and your good to write.
Step Four: Story and Plot
For porn, plot or story doesn't really 'matter' so to speak. There isn't any world-building or characterization. The majority of them will be tropes, you could put three chastity stories side by side and read the same character just with different names attached. Now, if you don't wish to think too detailed and just want to get right into the good stuff I'll list a few of the basic easy-to-follow plots that most stories will follow anyway.
The Cheater Plot: The story starts with the future sub/slave either by choice or by accident physically cheating on their SO. This would usually cause relationships to end, but instead, the SO insists they can make it work. But instead of the normal healthy method of therapy, they just go to the sex store and buy a device that puts the SO in charge of the sub/slave. After that, you can build off how you please.
The Cronic Masturbation Plot: Apparently watching porn and masturbating is considered taboo and 'cheating' to some. Never mind it's healthy and normal and could only be considered 'chronic' if you go to an actual therapist and get diagnosed with it. The solution for this as always is therapy and possible medication. But instead, the SO will just lock up their partner for 'their own good'. You can build the story off from there.
I'm into this Plot: So sometimes the Sub/slave will consent and WANT to be a part of the kink. They did their research they know what brands of cages or belts they want. They made sure they know how to clean and prepare ahead for themselves. All of this is an amazing build-up to an actual enthusiastic consent story. But sadly, the Dom/Mistress will step into the spotlight. The Sub/Slave hands over the keys blindly accepting and willing thinking the person they trusted this important piece of themselves to will follow the rules and be good keyholders. But instead, they somehow awaken an abusive and abrasive side to their SO. Who will ignore safewords, and 'unlock dates' because Fuck you I have the key now.