A cute and fun request from  superfun of the princesses being Starlight's diaper loving slaves. And why explain it on how it goes, when I can just tell you it with a story. Shall we?

Twilight appeared in Celestia's castle. She looked around in the throne room, seeing that it was empty. She was confused, using her magic to look at the note Celestia sent her, saying to meet her at the castle.
"That's odd, why isn't she here? Unless... Oh! Silly me, this must be a private meeting." Twi convinced herself, as she then headed off to the meeting room. However it was empty as well. She groaned. "Celestia?! I'm sorry to be frank, but is this another one of your pranks?!" She called out. After scanning the room, she noticed a secret passage way into a secret tunnel. Having no other way to ease her search, she went down the tunnel with the secret passage door closing behind her. Her horn glowed to light the way, walking down further and further till see was in a room. And odd room for that, but it had lighting at least. She eased her magic and then quickly took notice of a strange lime green jelly bean. "Huh? Now who would leave candy down here?" She then smirked. "Must be Pinkie Pie, only she would do something like this." She used her magic to pick it up and had it floated over to her. "Well, waste not, want not." She ate the bean, seeing that it did not tasted like a jelly bean at all. Before she knew it, it was too late. In a puff of smoke, her body started to transform, as something soft and crinkly wrapped around her waist. Right as the smoke cleared, she was coughing. "*Hack* *Cough* Well that was unexpected!" She wiped her brow with her arm, sighing for her coughing was done. Wait, arm!?! She raises both her front hooves, to see that they were no longer hooves, but arms with claws. "What the!?!" She then inspected her entire body, seeing that it was in a cat like form. "This can't be happen thi- ... Am I wearing a diaper?" She then stopped and saw a diaper around her waist. She blushes a bit, and then tried using her magic to take it off. It was no such luck, she didn't have a horn. So, she tried using her arms to take the diaper off, and to her surprise it worked with ease. Her diaper fell onto the floor with a crinkle. "Well, as nice as it was, I'm not in the mood for that."
"well I am." A voice spoke, surprising Twilight for she then felt a rope wrapping around her torso. It clung tight around her, lifting her up and turned her around to see Starlight, as a strange cat with the diaper that Twi found on her.
"Starlight!?! What are you do-"
"Hush little kitty, it's time for nap time." Her eyes started to swirl, for she was starting to hypnotize Twilight.
"No!" She started to struggle, grunting and wiggling but it was no use. Was far too strong somehow, so she had to look away from her gaze.
"Aww, don't worry Twilly, your friends are enjoying their kitty time." Starlight said, for her eyes then glowed and suddenly Celestia, Luna and Cadence appeared, all as cats and in diapers. Celestia and Luna were already far deep in the hypnosis for they were dancing and prancing away without a care, however Cadence was fighting it, but with little success. Then Twi felt the diaper wrapping around her waist again, but she was too in the trance to be blushing by this point. "And don't worry, I got more of those, jelly beans for you to have." Starlight smiled, as a tin of pills floated by her. Twi gasped and was soon diapered, the hypnosis kicked in as she was finally in full control. Her expression changed to a happy kitten grin, with Starlight finally able to place her down. She got on all fours and lowered her head down to stare deep into Cadence's eyes, then she giggled. "You always like playing the long game huh Cadence?" For which Cadence giggled a bit.
"You know me- *Grunts* -hypnosis from Chrysalis was more- *Huffs* -fun when me and Shiny resist's."
"Indeed silly kitty, but it's time to sleep." Starlight rubs Cadence's diaper with her tail, making her purr happily and finally fall into the hypnosis. "Now, it's time for you four to have some fun, I'm sure your fillies will take care of the castle well enough." Starlight smiled.

For those's how don't know, the idea of cadence and Shiny having hypno fun with Chrysalis is from here:
https://www.furaffinity.net/view/21150116/ Considering a shoutout pic.

I do not own any of the characters or the ideas involved with the pics, those are from the creators of MLP FIM and the artists themselves.
Anyway, hope you enjoy.