Sinful Nature
A Blue Exorcist AU by PupsIsMyDog
(Sinful Nature is when a person comits a sin and lets a demon related to that sin into the persons life. The person who lets it in is the only person who can rid of them)
Rin and his dear younger brother Yukio were winding down on a fine
Sunday evening. Today was the only day of the week where they had to
do absolutly nothing. No homework. No exorcisms unless they were
direly needed. No appointments or classes. Just one entire 24 period
when they could stop to enjoy life and talk like the brothers they
were. Technical civilized chats werent used at these times they had
together. But this time was a bit different than other Sundays.
Rin had been thinking about something all week to ask Yukio, but only
now did it seem right to ask. "Yuki" he began casually, "Why do you
always hide your tail?" Yukio shrugged at the question and put his
manga aside. "A demons weakness is his tail, so I try to keep it
concealed, as uncomfortable as it is" answered the younger sibling.
Rin frowned a bit a flicked his own tail. It was free. So free he
oftentimes forgot he had a tail. Yukio must be so uncomfortable; no
wonder he's so distressed all the time. Not only did he have heavy
responsibilities on his shoulders, but he carried out his duties in an uncomfortable state.
Rin got up and walked over to his brother, reaching in the back
of his pants. "Its Sunday. The one day we're free. So we should be
able to feel free too" He pulled out the tail, but let go instantly
when Yukio reacted. His face was flustered and he held a hand over his
mouth. "R-Rin, be more careful with it!" he whined. Rin pulled it the
rest of the way out gingerly, being sure to touch it as carefully as he
could. Once out, Yukios tail was nicer than expected. Probably because
it didnt hang out all the time like Rin's to give it a chance to get dirty or matted. The older brother smiled and petted the tail as if it were Kuro. Yukio reacted fast with a
sharp moan as he pulled his tail away. "Leave it alone Rin! Its
sensitive!" He barked. Rin backed away. He didnt bother his brothers
tail any more that day. But curiosity about it brewed in his mind all
week. What did Yukio mean by sensitive? Was he hurt? As the older
brother, it was Rin's job to find out.
All week Rin concentrated on how he would do this. He couldnt be too
passive, or Yukio wouldnt allow him to inspect. However, he didnt want
to seem too demanding either. When Sunday came around again and church
was over, he bagan his loose plan.
They sat across from eachother, reading manga or playing on their
phones as usual. About an hour into it, Rin put his phone aside and
looked at Yukio sadly. Once again his tail was trapped on a free day.
Just like last week, Rin walked over and started pulling it out. "What
did I tell you!? Its sensitive!" He shouted crossly. But Rin didnt
care. He inspected the tail, looking for ways that it might be hurt.
"It looks fine, how is it sensitive?" He alast asked. He rubbed the
tail softly, and only then did he get an answer. "It makes me all weak
and tingly inside, dang it!" Yukio half-whined. This somehow turned
something on inside Rin. Was Yukio's tail really an e-zone? He could
do something with this. He could tie Yukio down and force him to what
he wanted. He might not ever need to do homework again! And Yukio would either have to comply or else-Wait! Where were these thoughts coming from? They
were brothers! Yukio wasnt subject to Rin's every whim-but he could
be. Very easily.
Rin fought back and forth to the two voices. One told him this was
wrong; his sinful nature told him it was right. And, sadly, it was his
sinful nature on his demon side that won the battle. He jerked Yukio
out of his seat, red shine glowing from the depths of his eyes.
"Please Rin! Let me go! Let me go!" Yukio begged fearfully, but he was
no match for the stronger sibling. Yukio was very scared, and he had every reason
to be. Rin had never done anything close to this to anyone before. Rin began to take on his demon form as he pinned his brother. There were no flames, but his ears and fangs
had grown longer. His elongated tongue licked hungrily on his own
lips. Drool dripped from his mouth as he stroked Yukio's face with a single
sharp claw.
"R-Rin! Please! Please dont hurt me!" Yukio said at the
brink of tears. Rin only loosed a low growl and dug his nails into Yukio's arms. Blood dripped down his white shirt. "Now give me that pretty little tail of yours!" Rin
growled. Yukio shook his head and wrapped his tail tightly around his
leg. Rin hissed crossly, but smiled. He ran a claw across the surface
of the black tail, making Yukio cry out. "S-Stop! Im asking
you Rin! I know ive been hard on you, but I promise to better if you
let me go! Dont fall into your sinful nature! It will let other demons in, and God knows which ones!" Rin bursted into laughter at this. "Dear brother, demons cant always be on their best behaviour! And about being hard on me? Well youre doing that right
now!" He poked the growing bulge between his brothers legs, making
Yukio blush furiously. He couldnt be getting hard for his brother! It
wasnt right! But it couldnt be denied. And before he knew it, his tail
was in the clawed hands of a sinful devil. It was being rubbed base to
end, driving Yukio crazy. His back arched and he kept gasping, never
seeming to be able to get an entire breath. "Thats it. Come on. For
me" Rin hissed lustfully. He forgot about his original plan simply to see if anthing was wrong with his brother. Now all he cared about was making Yukio into his toy. The mere thought gave his demon side a jolt of excitement.
More attention was given to the base and tip of the little black
tail. Whenever a finger would push in and rub, Yukio would jerk or
moan loudly. "Thats it. Feel good?" Rin asked softly as he put the tip
of the tail in his mouth. Yukio almost screamed, and whined louder.
"P-please...Rin! Stop! I beg you!" He started wiggling furiously until even Rin couldn't hold him down. Yukio broke free and ran out of the room in terror. He ran out to the
city. Being as far away from Rin as possible was his top priority at the moment.
It was very late at the True Cross park, but when everyone else left, Yukio managed to stay alone in the dark thanks to the cover of a tree. He sat under the low-branched fir tree to keep out of sight. As he sat there, tears began to fill his eyes. "How could Rin let his sinful nature take him over?" He asked aloud, "Now thanks to him, more demons have been invited into the city!" Yukio sniffled more. As strong as he was in battle, sex had always been his weak point. Even talking to girls in a cute lovey way made him nervous as ever. "Why cant I be stronger..." he whispered, "Why can't I help Rin with the simplest of things. Such as falling into his sinful nature...?" "Why do you want to?" answered an
unfamiliar voice. Yukio instinctively reached for his gun, only to
find, to his horror, that they werent there. For the first time since
becoming an exorcist he officially was out of moves.
He went on quoting scriptures desperately, only making the voice chuckle lowly.
"Whats the matter son? Are you scared of daddy?" It asked. Yukio's
eyes flung open and he nearly had a panic attack. Was it
really...satan? Of all demons Rin could have let in?! Yukio stood, only to find
himself face-to-face with his nightmares. A very beautiful man with
elegant horns and slender tail stood there. His eyes were bright red,
his claws long and black. His terrible smile held despicable pointed
teeth, his ears were long but somehow handsome. His revolting tongue
licked his lips as he gazed at his younger son. "Surprise, surprise!"
he laughed, "I managed to take on my demon form in this world. How can I possibly thank your brother enough for falling into his sinful nature?"
Yukio hissed and thrashed his tail. He was still very afraid, but angry at himself for ever letting Rin do such a thing. "Ah, so threatening" satan said as he played with a ball of flame between his clawed hands. "But I escaped Rin before he could do anything. I guess just the thoughts he had were enough to let a beast like you in" Yukio snapped. satan hissed with pleasure. "So it scared you enough to make you run like a sick coward? Oh, you know how much I love fear. Especially that of my little son" Said the demon lustily. "Dont talk to me like that! I dont care that you got here, but go back to hell!" Yukio growled. satan swung his head back in laughter then looked at his son with an evil smirk. He slowly paced toward Yukio, who in turn took steps back. "Dont be scared of daddy. He only wants you to be good" satan continued to say. He could feel fear eminating from Yukio, and it gave him strength.
In one swift, unexpected move, satan grabbed Yukio's throat and pushed
him against the tree. He didnt choke the little one, but his grip was
tight for sure. Yukio grabbed the strong arms and cried silently. He
was terrified. After locking his blood father out of Assiah for a
year, how would the terrifying demon dad pay him back now that Rin allowed him in again? With death? Or would he keep him alive? Yukio's mind swam as the grip got tighter. "P-Please daddy..." he whimpered. "Say it again!" demanded satan.
"Please daddy!" Yukio squeaked. satan laughed and let go of his neck, but pulled
Yukio's form next to his body.
"I never thought I'd hear you say that. Now how about giving you more a reason to beg?" He pushed Yukio's back against the tree and draped the fragile legs over his
broad shoulders. Yukio didnt like this position much, but if satan
pulled away, he would fall painfully to the ground. "Now I get to
satisfy my own sinful nature; oh how long ive waited!" satan said as
he extended his tongue. It licked Yukio's pants between his open legs, bringing an
erection against his will. "Dont do this to me! Stop!" "No, I want
to see you squirm and call me by the cute name you gave me" "I'm not
going to call you that..." The tongue lapped at the sensitive spot. "Oh, daddy! Please!" Yukio squealed with a jerk. The demon king chuckled and kept licking. One of his hands grabbed his son's furry tail. Yukio, having never really been exposed to this sort of attention, reacted the only way he knew how; like a child taking a punishment. He cried out and did his best to stop satans menacing actions. But no matter how hard he tried, satan kept touching his sensitive spots as if there were no resistance.
"Where do you think all the
incubus learned their craft? You should know that youre helpless
against the one who taught them" Yukio tried to make a serious face,
but there was no way in Assiah he could do it right now. Every time he
furrowed his brows sternly, they bended back into a worried-like
expression. Every time he tried to make a threatening growl, it turned
into a straining moan. At one point he even tried to say something
threatening, but his voice was weak and breathy. As the minutes passed
it only worsened.
"I'm surprised you can hold out this long! However,
even the strongest of wills can be broken, as youre about to see. Moan
my name; I dare you" satan hissed softly. By this time his tongue had
found its place on Yukio's shaft inside his pants, and his hands became more expert at
their dirty work on the outside. It was all the young one could do to not break into
a writhing fit. He was close; constantly getting closer. His reactions
worsened and his tolerance was failing. How long until satan got his
sinful desire answered? "I can feel you trembling. I can see your
sweat. Stop fighting it and let it take you!" satan growled
impatiently. Yukio was about to go over the edge when a 3rd person
entered the scene. It was Rin Okumura with his flaming sword drawn.
He swung the sword, causing minor damage and making satan back away.
Yukio fell to the ground in a shaking mess. Rin hurried next to him
and comforted his little brother. "Im so sorry for what I did Yuki. I
didnt have control over myself. And by letting my sinful nature take
me, I gave satan leeway to get to you. Im so sorry, you have no idea"
Yukio said nothing but the sweet childish hug he gave said all that
Rin needed. "Come now sons! Surely you cant forget your daddy's here,
now can you?" satan said nervously. He tried to lay a hand on Rin, but
pulled back in agony. His hand sizzled with an invisible burn. Rin stood holding his younger brother, who was not the least bit afraid now.
"I'm sorry 'daddy'" Rin responded, "But there are only two
powers at work here: Love and fear. Love casts out fear, and without
fear you are powerless! So run home back to hell, we dont want you
here" He helped Yukio back to the dorm with a smile. Now not having any strength and being subject to the person who let him in, satan had no choice but to go back to where he came from.
"Thank you for
being a great big brother" Yukio said as he gave a sweet grin, "Just
dont go crazy on me again" Rin nodded. "Of course. I promise not to
touch you again unless you want me to" Yukio looked off into space for
a moment in thought. "Actually," he said slowly, "As long as you aren't
rough or scare the jeezers out of me, you can touch me any time you
want. It did feel a bit nice when you tugged my tail" Now it was Rin's
turn to go off into thought. These words were only things he heard in
his big-brother fantasies when falling asleep in class. "I'll keep
that in mind. Be sure to watch your back. I'll come when you least
expect"