Maybe just the tip

“H-how about just the tip.” Siara suggests as she looks into your eyes. “As long as you don’t break my hymen it’s fine.”
You want to grin but you fear that if you do, Siara will see. You don’t want to do anything to upset her so you maintain your composure and just grin inwardly. You slide in the tip in her until it touches her hymen and then pull it back out again. You do this over and over, fucking her with only the tip. Siara’s primed pussy yearns for more and makes her involuntarily buckle her hips. It pushes her pussy further onto your dick. Luckily you were just pulling back out so her hymen got spared.
“Ah, a little more, please.” Siara begs as she looks hopefully into your eyes.
You get the tip in just a little further. Stretching the abbess’s hymen until it is about to rip before retreating. Then you finish collecting demonic energy in your dick and you are ready to deflower this virgin.

You get your hands underneath Siara’s legs and raise them up. You help her wrap her legs around your waist. All the while you continue fucking her with the tip. Her virginity is so close to being destroyed, but you don’t want to be the one to it. You want it to be her.
“How is it?” You ask Siara. “Does it feel good?”
Siara nods.
You then hold your tip against her hymen and keep it there.
“Is it enough?”
Siara shakes her head.
You look into Siara’s eyes. She stares back into yours. She starts moving her hips.
Then she puts her hands onto your hips and whispers, “Please, forgive me father. For the flesh is weak.”
Siara then stares at her pussy while both pulling your hips towards herself and using her legs to push her hips to yours at the same time. Her actions cause your dick to get taken deeper inside her until, just as you wanted, her hymen breaks because of the actions Siara herself has taken. The intrusion of your dick into Siara’s teased core, as well as your demonic energy flooding into her, gives her a mini orgasm. Siara opens her mouth wide to moan. While she is moaning, the corruption floods into her and attaches itself to her body. Causing her lips and eyelids to darken and become black.
Now comes the time for you to prepare the next spell and fill your testicles with corruptive magic. In the meantime, you start ploughing the abbess’s virgin pussy while watching her moan and writhe in pleasure.
“Ooooh! This feels so gooood! Oh yes, get it in there! Push it into me! Your dick is amazing! I love it so much! Forgive me, lord. But please, fuck this slutty nun!” Siara moans loudly, her eyes locked onto her own deflowered pussy.
This is when you grant yourself the moment to smirk. The repressed slut has finally come out of the closet. The only issue you’ve got now is she’s trying to get you to cum before your balls have been charged with enough demonic energy. You try to slow down, but Siara’s legs prevent you from pulling away while her hips continue fucking you at a high pace. Maybe you should try distracting her.

“Hey, Siara.” You say. “Tell me the most perverted fantasy you’ve ever had.”
Siara looks up at you, her glasses now at the tip of her nose.
“One day, oh, I was watching, mmh, television and the movie, haaaah, had a girl, ah yes, and five guys wanted to date her.”
She quickly shoved her glasses back onto her nose and then continues her story.
“So, later that niiight, I masturbated thinking I had aaall five of those guys for myself. I had, ah fuck me harder, five hard dicks for me to sssuck on, slapping my face, aaahh, my breasts, my butt, and then all five of them, aaah I’m almost there, would cum all over my face and leave me a white sperm covered mess!”
Though her story kept being interrupted by her moans, you manage to hold in your orgasm until your balls were charged. Now you are ready to fully corrupt this nun and make horns sprout from her head.

You are about to tell Siara you’re close to climaxing, but instead she interrupts and tells you she is about to cum.
“Ooooh, John! I’m close! I’m so close! Oooh, fuck me with your demon cock!”
You smile and say, “Sure I’ll make you cum. But I’m gona, mmmh, cum inside you.”
“Yes! Oh please, yes! Cum inside me! I want to feel your heretic dick spurting inside my sinful pussy!”
With one hand on her breast and another on her hips, you start slamming into Siara hard and fast. Siara’s first response is to arch her back and cry out in pleasure. Then she starts thrusting her hips back at you while looking into your eyes and biting her lower lip. Hoping to receive your gift as soon as possible. She doesn’t have to wait long.
Soon your dick offers its first spurt of corruption inducing sperm into Siara’s pussy. Since you are fucking her so fast, you pull back again and slam inside once more. This time you stop thrusting and hold your dick inside her as you spill the rest of your corrupting seed into the nun’s womb. Siara arches her back again and screams in pleasure like a sex starved succubus who just received her fix. You feel her unexperienced pussy contract around your dick and suck in all of your corrupting dickmilk.
As Siara is orgasming in front of you, her veil starts to move. It gets pushed up, off her head, allowing plenty of her black hairs to spill out. Then you see that under the veil two horns are already growing. They start from just behind her hairline and push straight up, then start curling backwards in a wide arc. The further they grow, the more the veil gets pushed off her head. When her horns are finally done growing, they appear like those of a Capricorn. With her veil dangling on the end of one of them.
Once her orgasm finishes, Siara looks up to you and says, “Thank you.” Unaware that the gift you gave her is more than what she bargained for.