Warning: This story contains sexual themes, nudity, coarse language, and sexual intercourse. Reader discretion is advised.

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In the bustling city of Tenguu, amidst the ever-present threat of spacequakes and spirits, a quiet evening descended upon the Itsuka residence. Shido Itsuka, a young man with the unique ability to seal the powers of spirits through a kiss, sat on the couch, staring at the television without much interest. His mind wandered to his FOSTER sister, Kotori, who had been unusually distant lately. Kotori, the commander of the Fraxinus airship, was always busy with her duties, but something else seemed to be bothering her.

Shido sighed, stretching his arms over his head. "Where's Kotori?" he muttered to himself, glancing at the clock on the wall. It was past dinner time, and she still hadn't returned.

Just as he was about to get up and search for her, the front door creaked open. Kotori stepped inside, her expression a mix of fatigue and frustration. Her red ribbons, which signified her command mode, were tied firmly in her hair.

"Hey, Kotori," Shido greeted, his voice soft. "You okay?"

Kotori looked up, forcing a smile. "Yeah, just a long day." She walked past him, heading straight to her room.

Shido frowned, his concern growing. He followed her and knocked gently on her door. "Kotori, can we talk?"

There was a pause before she responded, "Come in."

Shido entered the room, closing the door behind him. Kotori sat on her bed, her eyes cast downward. Shido took a seat beside her, placing a hand on her shoulder.

"Kotori, you've been acting strange lately. Is something wrong?"

Kotori hesitated, biting her lip. "It's nothing, Shido. Just... work stuff."

Shido shook his head. "I don't buy it. You know you can tell me anything, right?"

Kotori looked up, her eyes glistening with unshed tears. "It's just... everything feels so overwhelming. The constant threat of spacequakes, managing the spirits, protecting you... It's all so much."

Shido pulled her into a comforting embrace. "You're not alone, Kotori. I'm here for you, always."

Kotori clung to him, her body trembling. "I know, but sometimes it feels like I'm the only one who has to bear this burden."

Shido stroked her hair gently. "We'll get through this together. You don't have to do everything on your own."

Kotori pulled back slightly, looking into his eyes. "Shido... there's something else. Something I've been afraid to admit, even to myself."

Shido's heart pounded in his chest. "What is it?"

Kotori took a deep breath, her voice barely above a whisper. "I... I have feelings for you, Shido. Not just as a brother, but something more."

Shido's eyes widened in shock. He hadn't expected this revelation. "Kotori, I..."

Before he could finish, Kotori leaned in, capturing his lips in a desperate kiss. Shido's mind went blank, his body responding instinctively. He kissed her back, his hands moving to cup her face.

Kotori's hands roamed over his body, tugging at his shirt. Shido pulled back, breathless. "Kotori, are you sure about this?"

Kotori nodded, her eyes filled with determination. "Yes, Shido. I've never been more sure of anything in my life."

Shido hesitated for a moment, then nodded. "Alright. But let's take it slow."

Kotori smiled, her hands still trembling. "Thank you."

As they stood there, Kotori's red ribbons seemed to glow in the dim light of her room. Shido's eyes wandered to her figure, noticing the changes in her body. Kotori had recently gone through a growth spurt, and her breasts had become significantly larger, now a voluptuous E-cup. Shido couldn't help but admire her curves.

Kotori noticed his gaze and smirked. "Like what you see?"

Shido blushed, looking away. "I, uh... yeah, you look amazing."

Kotori chuckled, pushing him gently onto the bed. "Good. Because I want you to enjoy every moment of this."

Shido's heart raced as Kotori straddled him, her hands running down his chest. She leaned in, her breath hot against his ear. "I've wanted this for so long, Shido. To feel your hands on me, to hear you say my name when you can't hold back anymore."

Shido groaned softly, his hands moving to her hips. "Kotori, you have no idea how much I've wanted this too."

Kotori kissed him deeply, her tongue exploring his mouth. She rocked her hips against him, feeling his growing arousal. "Then let's make up for lost time."

She started to unbutton his shirt, her fingers working quickly. Shido's hands moved to her blouse, slowly unbuttoning it to reveal her ample cleavage. Kotori shrugged off her blouse, her bra barely containing her E-cup breasts. Shido couldn't help but stare, his breath hitching.

Kotori giggled, pressing her chest against his. "See something you like, Onii-chan?"

Shido grinned, his hands moving to unclasp her bra. "I love everything about you, Kotori."

Kotori's bra fell away, revealing her large, perfectly shaped breasts. Shido cupped them gently, his thumbs brushing over her nipples. Kotori moaned softly, arching into his touch.

"Shido," she whispered, her voice husky with desire. "Touch me more."

Shido obliged, his hands exploring her body. He leaned down, taking one of her nipples into his mouth. Kotori gasped, her hands tangling in his hair.

"Yes, Shido," she moaned. "Just like that."

Shido switched to her other breast, giving it the same attention. Kotori's moans grew louder, her hips grinding against him. She reached down, unbuttoning his pants and freeing his erection.

Kotori looked up at him, her eyes dark with lust. "I want to taste you, Shido."

Shido's breath caught in his throat. "Kotori, you don't have to..."

Kotori silenced him with a kiss. "I want to. Let me."

She slid down his body, her hands pulling his pants and boxers down. Shido's erection sprang free, and Kotori licked her lips.

"Wow, Shido," she teased. "You really are big."

Shido chuckled nervously, his body trembling with anticipation. "Kotori..."

Kotori wrapped her hand around his shaft, stroking him slowly. She leaned in, her tongue flicking over the tip. Shido moaned, his hands gripping the sheets.

"Fuck, Kotori," he groaned. "That feels amazing."

Kotori took him into her mouth, her tongue swirling around his length. She bobbed her head, taking him deeper with each movement. Shido's moans filled the room, his hips bucking involuntarily.

"You're so good at this," he gasped. "So fucking good."

Kotori looked up at him, her eyes full of mischief. She pulled back slightly, her lips slick with saliva. "You taste so good, Onii-chan. I could do this all night."

Shido's breath hitched, his body on edge. "Kotori, I'm close..."

Kotori took him deeper, her pace quickening. Shido couldn't hold back any longer. With a loud moan, he came, his release filling her mouth. Kotori swallowed every drop, her eyes never leaving his.

As he caught his breath, Kotori crawled back up his body, kissing him deeply. Shido could taste himself on her lips, and it only fueled his desire.

"Kotori," he murmured against her lips. "I need you."

He moved lower, kissing a trail down her stomach until he reached the waistband of her panties. He hooked his fingers under the fabric, slowly pulling them down and revealing her most intimate area. Kotori shivered as the cool air hit her exposed skin, her legs spreading slightly to give him better access.

Shido kissed her inner thighs, his breath warm against her sensitive flesh. "You're so wet, Kotori," he whispered, his voice filled with desire.

Kotori whimpered, her hands clutching the sheets. "Please, Onii-chan... don't tease me."

Shido's tongue flicked out, teasing her folds. Kotori cried out, her hips bucking involuntarily. Shido held her steady, his tongue exploring her eagerly. He found her clit, circling it with gentle strokes that made Kotori moan loudly.

"Oh, Shido... don't stop," she begged, her voice breathless.

Shido increased his pace, his tongue working her clit with skillful precision. Kotori's moans grew louder, her body trembling with pleasure. She was close, her release building rapidly.

"Shido, I'm gonna..." Kotori's voice broke off as her orgasm hit, her body convulsing with intense pleasure. Shido didn't stop, drawing out her climax until she was a quivering mess beneath him.

As Kotori came down from her high, Shido moved back up her body, capturing her lips in a passionate kiss. She could taste herself on his lips, and it only fueled her desire further.

"Onii-chan, I need you inside me," she whispered against his mouth, her eyes dark with lust.

Shido positioned himself above her, his hands framing her face. "I love you, Kotori."

"I love you too, Onii-chan," she whispered.

He entered her slowly, their bodies moving together in perfect harmony. Kotori's moans were like music to his ears, her hands gripping his shoulders.

"Fuck, Shido," she gasped. "You feel so good."

Shido thrust deeper, his movements slow and deliberate. "Kotori, you're so tight... I can't hold back."

"Don't hold back," Kotori urged. "I want all of you."

Their lovemaking was intense, filled with whispered words of love and pleasure. Shido's hands roamed her body, memorizing every curve and contour. Kotori's nails raked down his back, her body arching into his with every thrust.

"Shido, I'm close," Kotori moaned. "Don't stop."

Shido's pace quickened, his release building. "Me too, Kotori. Come with me."

With a final, powerful thrust, Shido reached his peak, his release triggering Kotori's second orgasm. They clung to each other, riding out the waves of pleasure together.

As the intensity of their climaxes subsided, they collapsed into each other's arms, their bodies spent and satisfied. Shido held Kotori close, their breathing slowly returning to normal.

"Thank you, Onii-chan," Kotori murmured, her voice drowsy. "For everything."

Shido kissed the top of her head. "Always, Kotori."

As they drifted off to sleep, the bond between them felt stronger than ever. They knew there would be challenges ahead, but together, they could face anything. The flames of their love burned bright, illuminating the path forward.

--

The next morning, Shido woke up to the warm rays of the sun filtering through the curtains. Kotori was still nestled against him, her breathing soft and steady. He smiled, brushing a strand of hair from her face. She looked so peaceful, so content.

Kotori stirred, her eyes fluttering open. She looked up at Shido, a sleepy smile spreading across her lips. "Good morning, Onii-chan."

"Good morning, Kotori," Shido replied, kissing her forehead. "How did you sleep?"

"Better than I have in a long time," Kotori said, snuggling closer to him. "Last night was... amazing."

"It really was," Shido agreed, his fingers tracing circles on her back. "I love you, Kotori."

"I love you too, Shido," Kotori whispered, her voice filled with emotion. "Thank you for being here with me."

Shido held her tightly, their hearts beating in sync. They lay there for a while, simply enjoying each other's presence. Eventually, Kotori sighed and sat up, stretching her arms above her head.

"We should probably get up," she said, glancing at the clock. "The others will be wondering where we are."

Shido nodded, reluctantly getting out of bed. "Yeah, you're right. We have responsibilities."

As they dressed, Kotori couldn't help but tease Shido. "You know, I was thinking... Maybe I should get a new bra. My boobs have definitely gotten bigger."

Shido chuckled, pulling on his shirt. "Yeah, I noticed. Not that I'm complaining."

Kotori winked at him. "I figured you wouldn't mind."

They finished getting ready and headed downstairs, hand in hand. Tohka, Origami, and the other spirits were already gathered in the living room, chatting animatedly. When they saw Shido and Kotori, they immediately noticed the change in their demeanour.

"Good morning, Shido, Kotori!" Tohka greeted, her eyes sparkling with curiosity. "Did you sleep well?"

"Very well, thank you," Shido replied, exchanging a knowing look with Kotori.

Origami raised an eyebrow, a small smirk playing on her lips. "Something tells me there's more to that story."

Kotori blushed, but she didn't deny it. "Let's just say we had a long overdue conversation."

Kaguya and Yuzuru, the Yamai twins, giggled in unison. "Oh, we can imagine," Kaguya teased. "Just don't forget to keep it down next time."

Yuzuru nodded, her expression deadpan. "Agreement. Your voices were quite loud."

Shido and Kotori both turned bright red, eliciting laughter from the others. Despite the embarrassment, there was a sense of camaraderie and understanding among them. They were a family, bound not just by circumstance but by love and friendship.

As the day went on, Shido and Kotori found themselves working together seamlessly, their bond evident in every interaction. They supported each other, both in their duties and in their personal lives, growing stronger with each passing moment.

In the evenings, when the world was quiet and the stars shone brightly in the sky, Shido and Kotori would steal away to their private sanctuary. They would talk for hours,

sharing their hopes and fears, their dreams and desires. And when words were no longer enough, they would lose themselves in each other's embrace, finding solace and passion in their love.

Together, they faced the challenges that came their way, always stronger for having each other. Their love was a beacon, a flame that could never be extinguished, no matter the storms they weathered. And in that love, they found the courage to keep moving forward, knowing that as long as they were together, they could conquer anything.

Writer's Note: Thanks for reading. Hope that you readers enjoyed it. Please share this with others.