Chapter Text
You couldn't believe it. It was finally the best day of your life! Your eighteenth birthday! Your nii-san always had you live a sheltered life because being the little sister of a high profile pro-hero meant you were more susceptible to danger. He kept a close eye on you.
Today, he would have to do everything you wanted. It was written in the sibling contract. You were going to capitalize on this.
You barged into his room at 12:00 am on the dot and jumped on the bed.
"Nii-san! Wake up!" You said as you jumped up and down on the bed.
"Birdie, it's late, go to sleep." Keigo said groggily as he rubbed his eyes.
"It's my birthday. You have to do everything I say, and I want to play! If you don't want to play, that's fine. Just take me to Mina's house instead." You said the last sentence quickly.
You stopped jumping on his bed and sat over the blankets, by his feet.
That got his attention. He sat up in bed.
"Mina's house? This late at night? What for?" He said sternly.
"You never let me do anything. I'm a big girl now, and I should be able to do big girl things." You said with your arms folded across your chest.
"Big girl things like what?" He said as if he were about to scold you.
"I want to watch scary movies. And drink coffee. And maybe..." You looked left and right to make sure nobody would overhear you, even though you and Keigo lived alone together.
"Get a boyfriend." You whispered.
You hid with your face against the bed under his blanket after you said the last part.
"What do you need a boyfriend for?" Keigo said.
He was getting more and more displeased by the second.
"Nii-san... It's embarrasing." You curled into a ball and covered your face with your hands under the blanket.
Keigo pulled the blanket away from you and waited for your response.
"Well, you know... Things boyfriends and girlfriends do." You said as if it were top secret.
No. I don't. Enlighten me." He said as he breathed out through his nose angrily.
"Well. I want a boyfriend so we can text throughout the day. And sometimes maybe he can compliment my outfits? And maybe we can even"
You sprawled out on your nii-san's bed and had a dreamy look in your eyes. You started to speak more animatedly.
"We can maybe walk home together from school! And maybe if he's okay with it we can hold hands!" You started to smile.
"And... Maybe once a month we can kiss each other's cheek. And maybe once a year we can even kiss on the lips!"
You were blushing like a fool and grabbed your nii-san's pillow and started to hug it tightly. You needed to get this warm and fuzzy feeling in your chest, out.
Keigo chuckled. You were still a cute and innocent little thing. All his.
He knew this day would come. He had hoped it would have come after you graduated college instead. You were still in high school but it's to be expected. Mina was a bad influence on you. She was harmless but gave you all these progressive ideas which polluted your brain.
That's okay. He would correct your ways.
"I'll do all those things with you." Keigo said as he pulled you onto his lap and had you straddle him as you faced him.
He gently removed the pillow from your hands and smiled at you.
"I'll even be your boyfriend." He stroked your cheek with his fingertips.
You always listened to your nii-san. He knew what was best for you. He was also super cool and let you get away with stuff like eating candy before bedtime and even let you go to school. Most people in your situation didn't get to experience stuff like that.
You were lucky he was so nice to you and you always wanted to make him happy.
You weren't supposed to date your family though. You remember learning something like that from school.
You squirmed in his lap and shifted your weight from either knee and bit your lower lip.
"I don't think we're supposed to date family?" You said as you thought inquisitively.
"That's usually true but older brother and younger sister relationships are fine. If you were the older sis, or if I was your dad or if you were my mom it wouldn't be okay. But since I'm older than you and your brother, it's fine. I'm also only your half brother so it doesn't even count, really." He said.
You were gullible. If he told you the sky was pink you'd believe it. He did a good job keeping you sheltered and having you go to conservative schools. You knew that when your opinion or truth differed from a man's, especially a family members, the man's verdict was correct. It's just how everyone's brains are wired.
You started to stroke your chin and furrowed your brow.
"Um, okay. I guess it's okay." You said unsurely.
You moved to get off of your nii-san's lap but he wrapped his arms around your waist, pulling you closer to him so your chests were touching.
"Um, nii-san, can I get off of your lap now? This position is a little weird." You bit your lower lip.
"I need to teach you what boyfriends and girlfriends do together. You said you're a big girl now right?" Keigo said as he rubbed gentle circles on your sides.
You were feeling uncomfortable. This felt strange, even though your nii-san said it was okay.
"I'm scared." You started to breathe in quick shallow breaths.
He pulled you off of him gently and placed you on the bed next to him. He didn't want to frighten you.
"Birdie, there's nothing to be afraid of. I'm here for you and we'll go as slow as you want, okay?" He placed a hand on your face and stroked it soothingly.
"It's your birthday. You said you wanted to try coffee and watch scary movies right? Let's go downstairs and do that. How does that sound?" He flashed you a dazzling smile.
It was hard not to melt when you saw it.
You nodded and your breathing slowed down.
You went into your bedroom quickly and brought your favorite plushie and blanket with you before heading downstairs. You needed to be prepared. You've never seen a scary movie before.
You went downstairs and saw your nii-san with a cup of coffee in hand and the movie already playing. He looked really cool.
"Come on birdie. I made it sweet. It's practically a milkshake at this point." He said.
You sat down next to him and saw that it did look kind of sweet. It had whipped cream and sprinkles on top. He was so thoughtful.
You took the coffee from him and drank a small sip. The whipped cream was sweet but the coffee itself was bitter. You didn't like the bitter taste of the coffee. Everything else about the beverage was yummy.
You tried not to frown.
Keigo chuckled. He knew you'd hate coffee. You loved sweet things.
"It's okay. Coffee does take some getting used to. Let's watch the movie okay?" He spread his wings out and pressed you closer into his chest.
He put his arm around you and focused on the movie otherwise.
He was cruel and picked an especially scary one.
You were ten minutes in and were starting to feel scared. You pressed your face into your plushie and took deep breaths.
Keigo was jealous of your plushie.
"What's wrong birdie? Your boyfriend is right here. Hold onto me if you're scared." He said with a smile at you.
You moved your plushie to the other side of the sofa and you held onto your nii-san's broad arm instead.
His arm naturally fell in between your legs and you pressed your body into his arm, snuggling it like it were a body pillow.
Keigo's cock twitched.
You had to have been asking for it.
"How about we stop watching the movie? It's not really good."
You nodded.
He turned off the movie and noticed you were trembling.
"Is my baby bird scared?" He said to you in a kind manner.
"N-no." You said, trying to be tough.
"It's okay. I can help you forget about the scary stuff. If you want?" He said as he rubbed your thighs gently with the arm that was still nestled in between.
You sat up and untangled yourself from him.
"I don't want to bother you nii-san." You said as you looked over at your plushie for comfort.
Keigo put his arm up behind your head on the sofa and used his other arm to wrap around you, grabbing his own wrist with you in between.
"You're not a bother sweetie pie." He whispered.
His hot breath tickled your ear and you leaned away from him slightly.
You turned your face to him and saw him centimeters away from you.
He kissed your cheek softly.
You jumped a little.
"How was that?" He said as he stayed close to you. He shifted to rub your arm gently.
"That felt good." You said as you let yourself relax a little.
Keigo-nii was experienced. He knew what he was doing. He'd take care of you. He always did. You told yourself that you needed to just trust him.
"My good baby bird." He kissed your other cheek softly as well.
He had his eyes open the entire time and read all of your movements, felt your heartbeat and smelled your arousal building. He wanted to turn you into putty.
"Can I kiss you on the lips?" He asked. His golden eyes were soft and he waited until you gave him consent. He wanted you to have positive memories of him. Of this. Of everything.
You nodded.
He pressed his lips against yours softly. You unconsciously pressed your body against him and pulled away when you noticed yourself leaning into his touch.
"Sorry nii-san. I didn't mean to get carried away." You said as you tried to control your breathing.
"Shh. Just listen to what your body's telling you. Don't think so much." He said as he kissed you again but licked your lower lip gently.
You gasped as you were shocked with what he was doing and he took that as an opportunity to snake his tongue into your mouth. He was gentle about it and only stuck it in a little bit. He wanted to taste your saliva. It was so good.
His hand that was rubbing your arm began to rub closer towards the crook of your arm and rubbed up against your breast. It felt like a jolt of electricity through your body and you breathed in sharply.
Keigo pushed you a little further and groped your breasts completely. They were small as you hit puberty really late and were generally very petite. He knew it was a sore spot for you and he teased you about it occasionally. It was adorable to him. He had a little doll that was all his, that couldn't ever fight back. It made you even more perfect.
He tweaked your nipples over your pj's and you moaned softly.
"Sorry. I made a weird sound." Your eyes were lidded and you felt confused.
"It's okay baby. I like hearing it." Keigo said as he picked you up and had you straddle him again.
You were okay with it this time and smiled at him.
"My boyfriend is really cute." You whispered and buried your face in your nii-san's neck.
Keigo pulled your face away from his neck and kissed your lips with more passion. He grinded his hips up into your pussy. You moaned into his mouth.
"Nii-san...that feels weird." You squirmed a little.
He ignored you and opened the top few buttons of your pj's and exposed your tits to him.
"Your tits are so pretty baby." He said as he latched onto one of them and sucked on it gently.
He wasn't going to make you cum. He wanted to make you needy for him and dependent on him to cum. He was going to have fun toying with you.
He came back up to your mouth and made out with you. He pinched both of your nipples softly.
He stopped touching your tits and you whined at the loss of his touch.
"Use your words big girl." He teased.
You shivered. You weren't supposed to do things like this? Only mommies and daddies saw each other naked.
Boyfriends and girlfriends only kissed maybe sometimes.
Your nii-san was so nice. He gave you an opportunity to stop before you two went too far. You needed to take a cold shower to purify the thoughts that were plaguing your mind.
"Um... thank you nii-san! I have to go take a shower now." You said as you bolted up the stairs.
Keigo chuckled. He was going to have fun with you.
He sent a feather to follow you and brought back your panties that you threw in the hamper. They were unsurprisingly drenched.
He sucked on the crotch portion and drained every bit of your wetness out of them. He was hard as a rock.
He wrapped the crotch section around his cock and fucked his hand to your panties. They were white and had little strawberries on them.
He came soon after and cleaned himself up with your panties. He knew you were fighting an internal moral battle. He wouldn't push you. You were already so agreeable. Making you fully his would be easy. No need to scare you too much.