Makoto wasn't quite sure why it struck him that day.

He and Komaru were sitting in the living room watching anime like usual. The scene playing on their screen was a stereotypical, though still hot, fanservice scene of a girl with large boobs. Komaru never really seemed to mind, and in fact, sometimes seemed to enjoy it almost more than Makoto. This time, she was kind of just watching, however, and she let out a deep sigh that made her chest rise and fall.

A chest that, for no particular reason, caught Makoto's attention that day.

'Huh, Komaru's chest is as big as that girl's, isn't it?' He thought to himself. Little did he know that single thought would send him down a path that would change the rest of his life, and make the next few days a little bit of a hell.

It started off subtle; every time she made a drastic movement that made her chest bounce or jiggle, he would notice, but wouldn't give it much thought, like usual. But he began to notice it more and more. During dinner, as she told their parents about her day, her chest would move with her somewhat exaggerated movements. When she stretched, he would notice. He started to notice it even when she wasn't moving all that much.

Had they always been that big? If not, then since when? How had he not noticed before? Why was he noticing now? Why couldn't he stop noticing?

The thoughts even began to creep into his nightly masturbation sessions. One minute he was thinking about one of his many attractive female classmates, and then suddenly, Komaru would pop into his head. Her nude body in front of him, shaking her bare breasts for her big brother. Crawling towards him, grabbing his-

At first, he felt disgusted and horrified, and shoved the thoughts away. But after it happened the second time, and then the third…he started letting it stay. He let the fantasy play out. Imagined his sister blowing him, letting him play with her tits, letting him cum all over them. It was wrong, so wrong, but…why did it feel so good?

Things got worse during the next weekend. With their parents gone, Makoto and Komaru had the house to themselves, and because it was a hot day, Komaru decided to go without a bra under her shirt, something with Makoto very much noticed.

She sat in front of a fan that blew delightfully chilled air into her face and body. It made her nipples stand out from her shirt, and said shirt blew teasingly up, just barely exposing the bottom of her chest. Makoto had to excuse himself when he got a boner just from that.

That night was even worse. After her shower, she came out into the living room wrapped in a towel, yelling at Makoto about something with the soap. He couldn't really pay attention to what she was saying, since her large cleavage was just sitting there in front of his face. They bobbed with her, once again, dramatic movements, and the towel looked ready to fall at any moment. Unfortunately, or maybe rather mercifully, nothing happened, and after he said sorry, she went back to her room.

That night, he nearly cried out with how hard he came.

But that Sunday, everything came to a head.

After waking up that morning, yawning, sprouting morning wood, he got up and walked to the bathroom, half-asleep. Without bothering to check if someone was inside, he opened the door-

-only to find Komaru standing there almost completely naked.

Time froze as the two stared at each other. The girl's panties were around her knees, as she had been in the process of pulling them down. Her bare chest hung down slightly in front of her body, and Makoto's eyes, despite his best effort, shot straight to them, and his dick throbbed painfully in his pants as he let out a noise that was somewhere between a wheeze and gasp. Komaru began to tremble as she couldn't seem to move at first, and her face turned bright red.

"M-MAKOTOOOOOO!" She finally screamed and, shocked out of his stupor, he apologized and rushed out of the room, the image of her like that now seared into his brain. He couldn't stand it. He ran straight to his bedroom, and with a groan, yanked his dick out of his pants, and jerked off, harder than he ever had before. He didn't even care if Komaru chased him and found him like this. It felt so good. Her face, her breasts, the little bit he saw between her legs, it all flashed through his mind like a kaleidoscope of lewdness until he finally came, spurting onto his stomach as he experienced the strongest climax of his life.

It felt so good that he didn't even feel that guilty afterwards like he usually did.

A little time later, Makoto had settled back in the living room, watching some anime. He felt relaxed for the most part, though that image of Komaru was still locked in his brain for the rest of time. His sister slowly crept into the room, dressed in a large t-shirt and skirt. Her face was still red, and her hair was a still wet, as she'd likely just come out of the shower. "Makoto?"

"Y-yeah?" He asked. "S-sorry, I was still kind of asleep, so I wasn't really thinking about what I was doing or that another person might be in there, and then when I saw you, I just was so frozen I couldn't help but look and couldn't move so-"

"Stop." She said, putting an end to his rambling as she sat on the couch next to him, and fiddled with her shirt. "So you…saw?"

"Yes." He said, figuring it would be dumb to try and lie. "I…didn't see your um…groin…much, if that helps." Her blush deepened, and she cleared her throat, looking away. Neither of them spoke for some time. When she did finally speak, though, her words surprised him.

"Did you…like what you saw?"

Makoto's eyes shot to her own, and the image of her nude body popped into his head again. He gulped, unsure of how he should answer, so he simply told the truth. "Y-yes. Very much." Komaru's blush deepened, and she tried to force a smile.

"D-do you…want to see…more?" She asked, and his brain stopped working for a couple seconds. When it finally started again, he opened and closed his mouth a couple times like a dead fish.

"I…what?!"

"Makoto…I…um…" she hesitated, seemingly trying to find the words to say. "If you want to…look…you can ask, right now…and I'll show you. E-everything." She waited for his response.

"Wh-why?" He asked, extremely confused. She whined and shook her head.

"D-DO YOU WANT TO SEE OR NOT?!" She asked.

"Y-yes! Yes I do!" He said, and although he felt like he should take the words back, he couldn't. Komaru took a deep breath, and then exhaled. She grabbed the bottom of her shirt and lifted it up, and then off, revealing a lack of a bra underneath the shirt as her breasts bounced with the reveal. Makoto couldn't help but gasp at the sight of them. They were…gorgeous. In every possible meaning of the word, they were perfect. They looked even bigger than Aoi's, a girl who would often appear in his own fantasies. Her nipples were hard, and stuck out against her pale skin. Every movement she made caused them to sway. He stared in absolute wonder at them, and gulped.

But Komaru wasn't done.

She stood up, making her boobs jiggle even more as she turned around, and grabbed her skirt. After a moment of pause, she started to slowly pull them down. It was quickly revealed she also wasn't wearing any panties as the skirt slid down, revealing a bit of her ass crack, and then more, and more, her bountiful cheeks coming into view as she bent over, until she dropped the skirt entirely. Her legs were closed in a way that stopped him from seeing between them, but her ass was still right up in his face. She waited a little bit so he could get a good look at them, the boy tempted to reach out and squeeze one of the cheeks.

Finally, she turned back around and sat down, but in a way that still kept the space between her legs hidden, for now. She leaned forward and practically thrust her boobs in his face. "You can…touch them too, if you want."

"R-really?" He asked, and she nodded slowly. He knew this was wrong on every possible level, but he didn't really care anymore. His lower head was the one doing the thinking now, and he leaned in, thrust his hands out, and grabbed firmly onto both of the girl's breasts. The moan that came out of her mouth only accentuated his desire for her, and he began to squeeze.

His hands glided across her breasts, touching every single bit of skin he could find. He rubbed her nipples with every finger, watching as she thrashed and lurched, lewd noises escaping her lips as she gripped the couch. Makoto's dick felt painful as it pushed against his pants, wanting to be freed. She shuddered at just how soft her skin was, how much he wanted to keep doing this all day, if she would let him.

It was heavenly.

"M-Makoto…" She said, and he had to force himself to stop.

"Y-yeah?" He asked breathlessly. Komaru moved away from him and laid back on the couch. As she did, she finally spread her legs, lifting one onto the head and the other hanging off the side. Makoto's eyes went wide at the sight, and once again, his dick throbbed painfully. With her fingers, she leaned down and spread her lower lips. She was completely bare, allowing him to see everything, including inside. She was dripping wet with need and desire, and the way her voice trembled when she spoke again got that across even more.

"Put it in me, p-please." She begged.

He didn't hesitate. Within moments, his cock was out, and inside her.

The two engaged in the taboo act for hours, trying every possible position they could think of, doing it everywhere, on the couch, the floor, the kitchen table, the counter, the bathroom, the shower, their beds, everywhere. They touched each other's entire bodies, leaving nothing unexplored. They wholly and entirely gave themselves to each other, and by the end…they felt absolute bliss.

…Until their parents came home and found them fucking doggy style in front of the door.