Twincest voyeurism (Kaoru/Hikaru, Kyouya watching)
Hikaru started riding him before Kaoru had even managed to catch his breath. He took a deep breath, trying not to-- not to come immediately despite how hot and sweet Hikaru felt as he rode his cock. He moved a hand to the back of Hikaru's neck, bringing him forward so that he could kiss him, moaning into the kiss.
He felt when Hikaru got a hand between them both, felt the way his brother jerked off, realizing that Hikaru was also closer than he had thought-- he had had to be strung tight far more than he had realized, even with Hikaru dragging him to the music clasroom.
It was good, though, that they'd be coming soon. Although there was still time before the club opened, he didn't want to risk being caught despite the thrill of excitement that he knew both him and Hikaru felt at the idea. Hikaru broke the kiss, moaning against his neck, and Kaoru moved his hands to his brother's hips, thrusting into him as well as he could with Hikaru on top, hoping he'd last enough for his brother also to find his climax.
Before he could, however, they heard the door opening. They both turned around, frozen, finding out Kyouya there, unmoving despite the closed door. For a moment, Kaoru was uncertain on what to do, how to act, Hikaru also completely frozen over his lap. It wasn't until he saw besides the shock, some hastily-hidden flare unto Kyouya's eyes.
That made up his mind. They hadn't only managed to shock Kyouya, but perhaps, also excite him? He glanced towards his brother. Hikaru's hair was messed up, hard to tell them apart like that. Kaoru bit his lip to stop himself from grinning and instead made himself moan out loud, a pleasure he rarely indulged in, closing his eyes as he arched again, hands still against Hikaru's hips, leaning forward to lick his brother's neck. This was a different show they were used to, but he decided they were going to make the most of it anyway.
"Kaoru," he moaned, feeling the surprise run through Hikaru, the way his thighs tensed, how his brother turned to look at him. He felt his eyes over him and he gave a soft squeeze to his thighs, making his voice huskier. "Don't stop, Kaoru, please, I'm so close..."
Before he even finished, he felt Hikaru move again.
"A-ah!" Hikaru leaned backwards, hands against his knees as he moved again, letting go of his cock. Kaoru tried to think what Kyouya thought of Hikaru like that, the flush to his skin, his cock hard and already leaking pre-come. His brother moaned, voice breathy. "Hi-Hikaru! T-touch me, please!"
He moaned, reaching for his brother's cock, the feeling as familiar as his own, jerking him off hard and fast. From the corner of his eye, he saw that Kyouya hadn't moved. "Kaoru! Come for me, brother, come!"
Hikaru nodded. He rarely was verbal when on the brink of orgasm, but he still moaned, licking his lips. "I'm going, Hi-Hikaru, I'm going to... ah, feels so good, ahh, don't stop, please, brother, please, ah--"
He felt the way Hikaru's ass tensed around his cock a moment before his brother spilled on his hand. Kaoru would've loved to turn and see Kyouya's face but he had to let go of his brother's cock and hold his hips tight and hard to thrust into him, moaning as he came, too.
He felt Hikaru collapse against him, his face against his neck; Hikaru was never so loving and tender as after sex, and it was second nature for him to move his arms as much as he could and wrap them around his brother. Through the haze of his orgasm, he heard soft steps moving away and then the soft click of the door closing. Since Hikaru hadn't tensed at all, he didn't think his twin had heard, but he'd calm him about it later.
Kaoru wondered, though, how exactly would Kyouya use this information, and found the idea kind of exciting.