I've been meaning to write this story myself but I have been having issues with time and motivation to get it going.
My idea involves the main character of the story getting into trouble with magic of some kind. Be it a witch that they cross paths with or a succubus they release from a sealed tome or something otherworldly along those lines. For their efforts they'd end up unwillingly enslaved by this magic being and they'd be affected by magic writing on their body. This writing would essentially function as an enchant/curse and would affect them depending on what was written.
For example someone could write 'I am unable to dress myself' with a magic pen or magic ink somewhere on the main character's body and then that statement would become true and the main character would be unable to make heads or tails of regular clothing and need another person to dress them. You could make it as wholesome or sexual as you'd like with writing ranging from 'I feel calm and relaxed with a pacifier in my mouth' to 'I cum whenever I poop' and everything in between. It's pretty much fair game for where you want to take the story. It could be a nice loving experience for the main character as they're slowly eased back into a life of diapers and happiness or it could be a disgusting and humiliating experience as they're forced to wet, mess and cum in their diapers against their will.
If this story has already been written somewhere on the internet, please direct me to it because the mere thought makes me fucking diamonds.