David had always been protective of his stepsister, Ashley, especially since she was only 18 and still quite naive when it came to matters of the body. On this particular evening, Ashley had complained of a severe headache and stomachache, so David, being a responsible older brother, decided to take charge and use his medical knowledge to help her. Little did they know that this night would spark an unexpected exploration of their desires.

Ashley lay on her bed, her petite frame curled up under the covers, wearing a loose-fitting pajama set. Her long, dark hair spilled across the pillow, contrasting with her pale skin. David knocked gently on her door, a concerned look on his face. "Ashley, it's me, David. Can I come in?" He had a medical kit in hand, prepared for any eventuality.

"Yeah, sure," she replied meekly, her voice barely audible.

David entered the room, his tall, broad-shouldered figure filling the doorway. He noticed Ashley's discomfort immediately, her face flushed with fever. "How are you feeling, Ash?" he asked, his voice gentle and full of concern.

"Not so good," she whispered, her eyes glistening with unshed tears. "My head is killing me, and my stomach feels like it's on fire."

David placed the medical kit on the bedside table and sat on the edge of the bed, his eyes scanning her fragile form. "I'm going to take good care of you, okay? I studied emergency medicine, so I know what to do." His reassuring tone seemed to calm Ashley, and she nodded, her large brown eyes fixed on him trustingly.

"First, I need to take your temperature," he said, opening the kit and retrieving a glass rectal thermometer with a silver tip, filled with mercury. "This might feel a little strange, but it's the most accurate way to check for a fever."

Ashley's eyes widened at the sight of the thermometer, and she bit her lip nervously. "I've never had my temperature taken that way before," she admitted, her voice laced with apprehension.

"It's okay, I'll be gentle," David assured her, his deep voice soothing. "Just relax and let me help you."

Ashley nodded, her heart racing as she scooted down on the bed, exposing her delicate backside. She wore a black thong, the thin fabric disappearing between her soft, round cheeks. David's breath caught in his throat at the sight, but he quickly composed himself, focusing on the task at hand.

"Lie flat on your belly and lift your hips a little," he instructed, his voice steady.

Ashley complied, her heart pounding as she felt the cool air on her exposed skin. David carefully parted her thong, revealing her pink, puckered hole, tight and untouched. He lubricated the thermometer with some petroleum jelly, his fingers trembling slightly as he applied the cool gel to her sensitive skin.

"Just relax, Ash," he whispered, his breath warm against her ear. "This might feel a little cold, but it'll help me take care of you."

Ashley let out a soft whimper as she felt the tip of the thermometer press against her anus, her body tensing. David slowly inserted the glass rod, inch by inch, his eyes never leaving her face, gauging her reaction. Ashley's breath hitched, her body stiffening as the thermometer slid deeper into her rectum, a foreign sensation that both intrigued and scared her.

"You're doing great, Ash," David encouraged, his voice hoarse. "Just a little further, and then we'll know how to help you feel better."

With a final gentle push, the thermometer was fully inserted, the cool glass contrasting with the heat of her body. Ashley lay still, her breath coming in shallow gasps, her cheeks flushed with a mixture of fever and embarrassment. David carefully adjusted her thong, covering her exposed flesh, before setting the timer on the thermometer.

They waited in silence, David's hand resting lightly on Ashley's back, offering comfort and support. After a few minutes, the timer beeped, signaling that the reading was complete. David carefully extracted the thermometer, his eyes never leaving Ashley's face, watching for any signs of discomfort.

"There, all done," he said softly, his voice filled with relief as he read the temperature. "You definitely have a fever, little sister."

Ashley let out a soft sigh, her body relaxing as the thermometer was removed. "I feel so hot," she murmured, her eyes fluttering closed.

David smiled, his gaze softening at her vulnerability. "I have just the thing to bring that fever down," he said, reaching into the medical kit once more. He retrieved a small box, opening it to reveal two torpedo-shaped suppositories, their smooth surfaces glistening with medication.

Ashley's eyes widened as she saw the suppositories, her innocent gaze filled with curiosity and a hint of fear. "What... what are those?" she asked, her voice trembling.

David's throat went dry as he explained, "These are suppositories, Ashley. They'll help bring down your fever and make you feel better. It's a different way of taking medicine, but it's very effective."

Ashley's face paled, her eyes darting between the suppositories and David's face. "But... I've never... I mean, I'm a virgin..." she stammered, her voice barely above a whisper.

David's heart ached at her words, and he reached out, taking her hand in his. "I know, Ash. I'll be gentle, I promise. It might be a little uncomfortable, but it's for your own good."

Ashley nodded, her eyes brimming with tears as she trusted her older brother implicitly. David positioned her on her left side, her knees drawn up slightly, and carefully applied some more lubricant to the first suppository. He guided the torpedo-shaped medication to her tight, pink hole, his fingers trembling as he held it in place.

"Take a deep breath, Ash," he instructed, his voice steady despite his racing heart.

Ashley inhaled sharply, her body tensing as she felt the cool, slippery tip of the suppository press against her anus. David slowly pushed, his thumb applying gentle pressure as the suppository slid into her tight rectum, inch by inch. Ashley let out a soft cry, her body arching slightly as the unfamiliar sensation filled her, stretching her in a way she had never experienced before.

"Shh, it's okay, you're doing great," David whispered, his free hand stroking her hair soothingly. "Just relax and let it work its magic."

Ashley whimpered, her body trembling as she adjusted to the sensation of being filled from behind. David held the suppository in place for a moment, ensuring it was secure, before carefully removing his hand. He repeated the process with the second suppository, his movements slow and deliberate, his eyes never leaving Ashley's face.

"There, all done," he said, his voice filled with relief as he disposed of the packaging. "Just rest now, and let the medicine do its job."

Ashley lay on her side, her eyes closed, her breathing ragged as she processed the intense sensations coursing through her body. David couldn't help but admire her delicate form, the curves of her hips and the swell of her breasts beneath the thin fabric of her pajamas. He felt a stirring in his loins, his desire for his stepsister growing with each passing moment.

The night passed, and Ashley's fever subsided, thanks to David's attentive care. As the morning light filtered through the curtains, Ashley stirred, her body aching from the unfamiliar sensations of the night before. David, who had dozed in a chair beside her bed, woke at her movement, his eyes immediately checking on her.

"How are you feeling this morning, Ash?" he asked, his voice rough with sleep.

Ashley stretched, her body still sore, but the fever had broken. "Better, I think," she replied, her voice raspy. "My head doesn't hurt as much, and my stomach feels calmer."

David smiled, his gaze filled with pride at his successful treatment. "That's great to hear. I think we should take your temperature again, just to be sure."

Ashley's eyes widened, remembering the intimate process from the night before. "Do we have to?" she asked, her voice small.

David nodded, his expression serious. "It's important to monitor your fever, Ash. Trust me, I'll be gentle."

Ashley sighed, her cheeks flushing as she lay on her belly once more, her thong-clad buttocks presented to David. He retrieved the thermometer, his hands steady as he prepared to take her temperature again. This time, Ashley's body was more relaxed, her muscles yielding to the familiar sensation of the thermometer sliding into her rectum.

David watched her closely, his eyes taking in her every reaction as the thermometer did its work. After a few minutes, he carefully removed it, checking the reading with a satisfied nod. "Your fever is definitely breaking, but I want to give you one more suppository to be sure."

Ashley's heart sank at the thought of another intrusion, but she nodded, her trust in David unwavering. He prepared the final suppository, his hands moving with practiced efficiency as he applied lubricant and positioned Ashley on her side.

"Just relax, Ash," he murmured, his breath warm against her ear. "This will make you feel even better."

With a gentle push, the suppository slid into her waiting hole, her body accepting it more readily this time. Ashley let out a soft moan, the sensation both relieving and arousing, her body responding to David's touch in ways she didn't fully understand.

David disposed of the packaging, his eyes never leaving Ashley's flushed face. "You're doing great, Ash. Just rest now, and I'll check on you later."

As he turned to leave, Ashley reached out, her hand grasping his arm. "David, wait," she whispered, her voice laced with uncertainty. "I... I have questions."

David's heart raced as he turned back to face her, his desire for her palpable. "What is it, Ash? You can ask me anything."

Ashley's eyes searched his, her expression a mix of curiosity and desire. "I... I liked it, what we did. But I don't understand why it felt so... good."

David's breath caught in his throat, his body responding to her words. "It's natural, Ash. Your body is discovering new sensations, and it's reacting in a very normal way."

Ashley bit her lip, her eyes never leaving David's face. "Can we... do it again? I want to feel more."

David's resolve wavered as he fought against his own desires. "We should wait, Ash. Your body needs to heal, and we need to be careful."

Ashley's face fell, her disappointment evident. "But I trust you, David. And I want to explore this with you."

David's heart pounded in his chest, his resistance crumbling in the face of Ashley's innocent yet enticing request. "Okay, Ash. We'll take it slow, and we'll explore this together."

With that promise, David left Ashley's room, his mind racing with thoughts of their forbidden desires. The morning's events had ignited a flame between them, and David knew that their relationship would never be the same again. As he walked away, he couldn't shake the feeling that this was just the beginning of a passionate and taboo journey, one that would test the boundaries of their step-sibling bond.