Now, a few things to clear up before we move on to what I'm sure you'd rather read. First off, just because Hiei insults Kuwabara all the time doesn't mean he thinks him inferior. Hiei wouldn't bother insulting Kuwabara if he thought he was inferior. Rather, Hiei thinks that Kuwabara has potential but is rather dense about it at times and it is how he pushes him. And, Kurama wouldn't waste his time training Kuwabara if he was 'useless.' He also sees potential in the boy but thinks that he wouldn't be interested or react well to a sexual overture. And, just because Yusuke's given up on the idea of Kuwabara being more than his best friend doesn't change the fact that Kuwabara is his best friend. His 'more' interest in Kuwabara wasn't strong enough to ruin their friendship when it was supplanted by the fulfillment he found with Kurama and then Hiei. He was really wanting to be with someone who'd understand him rather than with Kuwabara specifically. So, just because Kuwabara is a bit slow on the uptake and thinks this might be an elaborate game (consider that he's seen Yusuke and the Toguros come back to life, though with the later, it was part of a plot device to get them to the Ankokubujutsukai, and he's seen demons and traveled between dimensions and gained a super power. What part of this doesn't sound like a video game?), but that doesn't change the fact that he's giving his best and is, despite his 'flaws' of still going through puberty, an upstanding person. So, just because he is narratively at a disadvantage does not mean that he is inferior. It just allows you, the reader/viewer to see how far he progresses to keep up with those who are at a natural advantage. He probably overcomes more than the others do just to be where he is with them, or, in other words, Kuwabara is 'fucking metal, man.'
So, let's move on to what you want to read.
Kurama led Hiei to his room, pressing a hand against the door after it closed to encourage plants he'd seeded the wall with to thicken as they would soundproof the room. This became more important because Hiei enjoyed making him scream as much as possible. He enjoyed it, too, for the deeper relief it provided than just sex, a relief that almost reached to the very core of his being.
"You've been pushing that human," Hiei said, his hands working on removing his cloak, tossing it carelessly over Kurama's desk chair.
Kurama worked his own clothes off mater-of-factly, folding them on the desk. "Yes, but we only have a month and we need him. It would be better if there was more time to properly build him up and to bring understanding, but we only have so much to work with." When he was free of clothing, he walked over to his bed and bent over to offer Hiei a more enticing view while he worked the chains from under the mattress. While he could grow ropes that would hold him, Hiei preferred restraints that took a little more work to turn on him.
Hiei leaned against the wall, bare to the waist, his shoes off, but his pants still in place. "True," he allowed. "Do you think he'll understand once we're at the tournament?"
Kurama turned around flicking his hair over his shoulder, crossing his arms over his stomach just because it was comfortable. "Maybe," he shrugged. "He will fight, though," he added.
Hiei nodded then pushed away from the wall. He brought his hand up and backhanded Kurama hard, flinging the redhead across the room so that he hit the wall.
A smirk curved Kurama's lips as he pushed himself up. So, it was going to be like that? He liked it when Hiei hit him like this. He knew the petite powerhouse would never actually fight him, knowing that when Kurama fought seriously, he fought dirty and to win. But, Kurama enjoyed feeling the power of the one who wanted to dominate him and Hiei was very good at showing that power to him. Kurama's head hit the ceiling and he landed against the adjacent wall, his ears ringing a little from the impact. He shook his head and licked his lips, a gasp escaping them when Hiei grabbed his hair and pulled his head back, pulling him up onto his knees and then arching his back to present his throat to Hiei's bite. Kurama's toes curled as his airway was cut off and he became more aroused than he had been in a while. His mind went fuzzy and warm and the next thing he was fully aware of, his legs and hands were tied down to the head of the bed, his legs pulled over his body. Hiei was fast and good, he thought to himself as he tried to ease himself into a slightly more comfortable position.
Hiei smacked Kurama's ass. "I didn't say you could move," he said sharply.
"Sor—" His apology was cut off as Hiei wrapped his hand around his throat.
"I didn't say you could talk." Hiei slipped his legs over Kurama's so that he could straddle his waist, pushing at Kurama's joints uncomfortably. Had he truly been human, Kurama's legs probably would have been dislocated. As it was, his demon nature made it so they just hurt. He leaned over, pulling Kurama's hair, lifting his head so that his shoulders were pulled into a more uncomfortable configuration. "Imagine, next time I do this to you, that detective will fuck your ass like this," he growled out. He reached behind himself and guided Kurama's cock into his ass. "I'll have him beat your ass then fuck you hard."
Kurama moaned in pleasure and in pain, though it was difficult to know which was stronger. He tried to rock into Hiei's body, the demon's words filling him with lust and making him want to know what Yusuke's cock would feel like in his ass, how the boy would 'punish' him.
"I'm going to show him just how much of a slave to pleasure you are, how much you want pain," Hiei continued, seeing his words working their way into Kurama's mind. His hands went to the redhead's chest and he dragged his nails down, breaking Kurama's skin in eight lines from collarbone to nipple, drawing out a scream as Kurama arched into the touch, twisting his body more painfully in the awkward position Hiei had him in.
Hiei leaned forward, waiting until Kurama's eyes cleared a little. "Then," he said, his hands moving to Kurama's throat, his thumbs caressing the so vital pulses, "I'll tie him down and fuck him as hard as he fucked you while you're forced to watch, unable to do anything else because you're still tied down."
Kurama's hips rocked into Hiei's body, causing him to groan again. "Please," he whispered, the sound not leaving his throat as his lips formed the word.
"Speak," Hiei ordered, smacking Kurama.
"I…I want you both to fuck me, at the same time," he said, his mind and body burning with need. "I…I want both your cocks in my ass," he said, licking his lips.
"Then train the detective," Hiei spat, rocking back sharply onto Kurama's cock. He looked at the redhead, sweating freely, face contorted with pleasure and pain and lust. "Use one of your plants to fuck yourself," he ordered. "And no more talking. The only sounds I want to hear from you are those you cannot hold back."
With a will, Kurama obeyed, a seed from near the foot of his bed exploding to life, smaller vines reaching to caress his ass before a larger, round-tip vine forced its way into his ass. He screamed as Hiei reached back and pushed it in farther then pull it out, matching his timing as he rocked back and forth on Kurama's cock. The redhead's screams came more freely as his body began to tense.
Hiei smirked, his own pleasure building as he watched and heard what he was doing to Kurama. "At the tournament, when we have a chance, let us both fuck the detective," he whispered. "Together, the first chance we get, the three of us are going to fuck for as long as possible," he growled.
"Yes," Kurama screamed, his mind almost making him believe that Yusuke was there with him. The small vines began to smack his ass, leaving behind their little marks.
Hiei clawed at Kurama's chest and abdomen, leaving more bleeding marks behind as he did. "You will be ours to humiliate," Hiei continued. "I will teach Yusuke how to use you properly, thoroughly. Prepare yourself."
Kurama's eyes rolled back in his head and he arched, screaming as his joints protested, as his hips thrust into Hiei's body and he came with the image of Yusuke and Hiei jacking themselves off until they came on his face, making him suck their cocks hard again.
When he opened his eyes, he smiled lazily. Hiei's come was on his face and, even though the petite demon had released his legs, his arms were still connected to the bed. His eyes focused on Hiei, kneeling over him, enjoying looking up at him around a half-hard cock.
"Suck it," Hiei ordered, pulling Kurama's head up. He spent the rest of the night fucking Kurama, having Kurama fuck him and spinning fantasies involving the three of them together until they were both well satisfied with themselves.
Kurama stretched, his joints protesting, when Hiei released him. He kneaded his shoulders and his hips. "Care to join me for a shower before we head out?"
Hiei grabbed Kurama's arm and thrust him toward the bathroom. "Let's hurry. No sense in making Kuwabara wait."
Kurama allowed Hiei to move him. "Once we leave, I'll have to respond in kind."
"I'm not stupid enough to try this without your permission. And if the detective is, he'll soon learn." He shoved Kurama's back, causing him to stumble a little.
Kurama turned, his back against the wall, his legs spread, knees bent to lower himself, rolling his hips, his cock hardening. He licked his lips. "He will," he purred.
Hiei crossed the room, lifting Kurama's legs, adjusting him so that he could comfortably hold up the kitsune, then, as Kurama guided his cock, thrust in hard.
Kurama moaned, turning on the water and washing Hiei's hair then his own as Hiei fucked him against the wall. He then fucked and washed Hiei as the petite demon kept his hands against the wall and presented his ass. The rested in the tub for a few moments, just sitting next to each other for the time being.
Kurama yawned, stretching as he rose from the tub. "It's time to go," he sighed. "It's time to return to preparations."
"I have somewhere else to be tonight."
Kurama looked over his shoulder, a towel in his hair. "We have no commitment, Hiei. You're welcome when you have time and if you don't, that's fine as well. I enjoy your company and you are very adept at fulfilling me, but I do know better than to trap you."
Hiei nodded sharply, taking a towel and drying himself off quickly. For Kurama to call him 'very adept' was more of a compliment than he'd ever received from the kitsune and he wasn't quite sure how to react, so he wanted to leave quickly.
Kurama finished drying off and dressing, grabbing a quick breakfast before he headed into the forest. He was tired, but it wasn't enough to affect him and he knew he'd probably bought himself a week before Hiei was ready to fuck him again and the petite demon would strive to outdo himself the next time they spent time together.
In such a manner, the month passed for the three who remained behind. Kuwabara's endurance improved and Hiei received more compliments.