How do you do something right, if you don't know what's wrong?
It had been a nagging thought at the back of Celestia’s mind. Like an itch that she just couldn’t quite scratch. Despite the fact that she knew that everything was normal, she also knew that that wasn’t quite true.
Ever since Starlight had cast the spell that she’d created, an unnoticeable tide had been washing over Equestria. Everyone who came in contact with Starlight, got influenced by the spell. The thought of having sex with Starlight became as normal as having a conversation, or a handshake. Everyone affected would become attracted to Starlight, have sex with her, and then be unable to register the act being unusual in any way, even once they left her presence.
Anyone who saw it happening and intending to found out what was going on, usually ended up ensnaring themselves too once they came into close proximity. The current victims happily fucking Starlight, as well as each other.
As far as Celestia knew, Twilight had been the first victim. Which made sense, considering they lived together and Starlight probably immediately wanted to show off the spell to her, thus ensnaring Twilight to want to fuck Starlight every time they met.
Starlight was as much a victim of the spell as much as anyone else, however. Unable to realize how unusual it was for everyone she met to want to fuck her, and doing so happily herself, she never realized exactly what her spell had done. Over time, the spell dropped from her mind as she thought of other ways to impress Twilight.
Celestia had been spared from the spell’s effects for weeks, until Starlight had asked for a private audience with the princess. If anyone knew something that might impress Twilight, then it was the mare that taught her almost anything she knew. Celestia had accepted and while seated at a table in her study, they had spent the afternoon thinking of alternatives. Uninterrupted apart from when Celestia dropped below the table, removed Starlight’s panties from underneath her skirt and ate her out.
They had parted late in the evening, Celestia gladly offering more chances for them to talk and figure out Starlight’s options. Unaware of the spells effects, all those meetings similarly contained the same carnal interruptions.
The spell avoided detection for a few more months, partly due to Starlight rarely going outside. Eventually enough ponies had witnessed the spell’s effects, without being affected themselves however, that word reached Celestia through some worried ponies. Their worries only increased once Celestia commented that she failed to see anything unusual about the spell.
Through repeated tries, Celestia was convinced of how unusual wanting to have sex with Starlight was, only for it to slip her mind relatively soon afterwards, considering it normal until realizing it once more.
Now, Starlight was imprisoned. As much for her safety as the safety of others. Her needs tended to by volunteers, willing to subject themselves to the spell until a cure could be found. And if ever Celestia felt like she wanted to fuck Starlight, she’d remember that she was in prison, question why, and realize once more that it was unusual to want to fuck her.
Starlight… wasn’t Celestia’s problem however.
Celestia’s problem was the pony that had intruded on one of her and Starlight’s meetings, and happily joining with both fucking Starlight and Celestia as the spell affected her too. Ever since then, the thought of fucking her dear little sister, Luna, felt as normal as breathing.
After Celestia was made aware of Starlight’s spell and its effects, she realized, after a quick comparison with memories of how she used to think about Luna, that wanting to make her sister scream in orgasm was not normal. So she wisely kept it to herself, as she dealt with the most pressing issue of Starlight.
This put Celestia in the unfortunate position of having nobody to rely on to help her remember what was strange or what wasn’t. She couldn’t just imprison Luna like she did Starlight, no questions asked, putting aside the thought of how hot Luna would look, completely restrained and helpless.
So for now, Celestia only had herself to depend on, and the thoughts that’d forever be slipping from her mind at a moment’s notice. She just had to remember that wanting to fuck Luna was unusual. Nobody should find out. It wasn’t normal. forbid-
A muffled moan shook Celestia out of her thoughts, and drew her attention back to the pony below her. “You’re doing great, Luna,” Celestia cooed as she thrust forward, pushing her white strap-on deeper into her sister’s pussy. She moved her hands across Luna’s bound body, resting them on her tits, before playing with her nipple piercings.
“Two months of training and your cunt already feels as if this cock belongs in it.” Celestia emphasised the point by giving another shove, fully hilting the strap-on and releasing another moan from her captive sister. “Just a few more weeks and you’ll be your sister’s slut in every sense of the word.”
Despite being gagged, the smile that graced Luna’s face was plain to see. She kept mumbling however, which told Celestia that she was trying to say something. Using her magic, Celestia untied the gag, easing the drool-covered ball out of Luna’s mouth.
“I’m glad my- hah! - my carnal training pleases you sister,” Luna said, straining against her bonds as her orgasm approached. “But I must say you seem distracted. W-wh- ah! - what troubles thine thoughts?
Celestia’s movement slowed as she tried to recall her previous thought process. Making sure to keep the strap-on moving in and out of her sister’s cunt, she tried to form her words. “I… I was thinking of how hot you look when tied up, dear sister. And… how much I love to make you cry out with pleasure.” Yes, that sounded right.
“If this vigor of yours is the result, then I shan’t argue with it,” Luna responded, barely able to keep the sentence flowing. As soon as she finished, she reached her climax, her pussy desperately clinging on to Celestia’s rubber cock, refusing to let it go.
Celestia responded by driving it as deep as it could go, pushing Luna further over the edge, prolonging her orgasm. As she made Luna hers, showing Luna that she belonged to her sister, she couldn’t help but feel a thought nagging at the back of her mind.