Technically the strongest human in the series, Sensui was a prodigious Spirit Detective that had a clear sense of what was considered to be right and wrong until he witnessed the Black Black Club torturing demons just for their own entertainment. This event not only caused Sensui to do a complete 180 and be ashamed of his own species, it also resulted in the development of his dissociative identity disorder, creating 6 other personalities in order to cope with what he had witnessed. With his complete mastery of martial arts in the form of Resshūken, his Sacred Energy, his Offensive and Defensive armors, and his various other techniques, Sensui clearly shows that his power is right in the mix of the S-class demons, especially during his fight with Yusuke. One thing to remember is that all if these demonstrations of power Sensui performed were done while Sensui was ill to the point where he was dying; had he not been ill, it is possible that Sensui at his absolute peak could reach the S+ ranking. At the very least, Sensui is certainly one of the strongest villains Yusuke ever encounters, and in the end is only defeated by Yusuke because of Raizen’s help, proving to be an incredibly formidable foe.

As one of Yusuke’s closest allies in his many battles, Kurama is a powerful opponent not only for being able to transform into his original demon form, but also because of his incredibly clever tactics as a fighter. Kurama grows quite a lot from the thief with a heart of gold we first saw. Many of his fights involve him keeping a calm manner as he observes his opponents’ fighting styles and personalities for weaknesses and capitalizes on those weaknesses. In the Makai Tournament (the tournament that ends the show), Kurama’s last major fight is in the 3rd round against Shigure, where he transforms into his S+ ranked Yoko form. Even though he doesn’t sustain this and is weaker in his regular form against Shigure, it is because of his clever ingenuity that Kurama is able to win the fight, showing why he deserves to be mentioned along the best of the best.

The wife of Enki, Kokou gives off an interesting impression by constantly drinking, consistently having a foul mood, and even insulting Raizen’s lover (mainly because she herself loved Raizen). However, she demonstrates her true strength through her participation in the Makai Tournament, with her most notable achievement being the one who defeats Yomi, one of the 3 Kings and the main antagonist in the last story arc. The fact that she was strong enough to defeat Yomi as well as Yomi’s indication of Kokou (and her friends) being close to him in terms of physical strength both indicate how Kokou can go the distance with the most elite demons. It makes you wonder just how further in the tournament Kokou could’ve progressed had she been in proper fighting shape.

The twin brother of Natsume, Kujo was one of Raizen’s former sparring partners back when Raizen was in his prime. Kujo, along with Raizen’s other powerful friends, is introduced to Yusuke when they come to pay their respects to Yusuke’s ancestral father, Raizen. Although he comes across as somewhat cocky, Kujo certainly proves that he can back up his talk. Kujo first begins his performance in the Makai Tournament with the defeat of the newly powered up Touya despite being both out of shape and even weakened significantly by Touya. Even with these handicaps, Kujo would go on to not only be the one who eliminates Kurama, but also defeat Kokou, a fellow S+ demon. Even though he eventually loses to another of Raizen’s friends (Saizou), Kujo shows that he’s right in the mix amongst the most powerful S+ demons.

The first legitimate villain Yusuke faces in the series, Hiei eventually works together alongside Yusuke (even if it’s for his own motivations at first). Hiei also grows a lot throughout the series, as he struggles to balance his friendships with his desire to gain more power, not to mention do whatever it takes to protect his twin sister Yukina. However, it is Hiei’s fighting style and techniques that mark him as arguably Yusuke’s strongest ally. With the insane speed that he possesses, the multiple fire and swordsmanship techniques he wields, the techniques that come with the Jagan Eye, and the fact that he’s the only demon to master the Dragon of the Darkness Flame, Hiei proves time after time again that it is very hard to defeat him. This is best evidenced by his quick dispatch of Seiryu, his undefeated record in the Dark Tournament, and his fight against Mukuro, where despite being outclassed by her, Hiei is able to destroy once and for all, Mukuro’s shackles, severely handicapping Mukuro’s true power level and ultimately preventing her from winning the Makai Tournament. That honor would instead go to…

Enki is considered to be the leader of Raizen’s group of friends that return to honor Raizen. A gentle soul, Enki’s strength is perfectly demonstrated by the fact that he was able to win the Makai Tournament, thus becoming the new king of Demon World. Although it might not appear that Enki really strained himself in his matches, it’s evident that Enki certainly didn’t coast to this title, as he was able to beat many of Raizen’s friends along the path to the title. In addition, Enki’s most notable feat of the tournament was being strong enough to be the one to defeat Mukuro, another of the 3 Kings. Out of all of Raizen’s friends, Enki is certainly the best in terms of being able to be on par with the 3 Kings.

Yusuke’s growth throughout the series is incredible when you think about it; going from being a regular kid to being one of the most powerful “demons” ever is a remarkable transformation. Yusuke certainly learns a variety of Sprit techniques that he uses to defeat his many opponents, and those techniques combined with his unique fighting style make him very formidable. However, despite Yusuke’s training over the course of the story, he dies for the 2nd time in the series at the hands of Sensui. It is only when Raizen revives him in a newly awakened demon form that Yusuke attains the rank of S class. Both Raizen’s possession of Yusuke in order to defeat Sensui and Yusuke’s performance against Yomi in the Makai Tournament demonstrate that Yusuke is certainly stronger than most of the S+ demons. One can only imagine just how much power Yusuke will obtain once he is an adult, as the series ends with him having the potential to become the most powerful character in the series.

One of the 3 Kings, Yomi’s power is recognized and feared by many in Demon World, as he rules his own country and has several S demons that work under him. Even his old friend Kurama returns to him to be his right hand man. Although many of his feats are talked about, the best demonstrations of Yomi’s power are through his fights with Shura and Yusuke, as he shows how effortlessly he can beat an S ranked demon and narrowly defeats Yusuke in a match full of their best techniques. As a result of this match, Yomi ends up losing his next match to Kokou. Nevertheless, Yomi’s combination of powerful techniques, intelligence, and the way he can sense the world around him make him one of the most powerful S+ demons.

Arguably the most powerful character in the series, Mukuro is another member that makes up the 3 Kings. Mukuro’s backstory is one filled with tragedy and sadness; however, it leads to Mukuro obtaining power few have ever known, causing other demons to rightfully fear her. Mukuro’s power is directly related to her state of mind; as a result, the angrier she is, the more powerful she can become. However, Hiei was able to severely limit Mukuro’s power during the Makai Tournament when he destroyed the shackle on her left wrist, a powerful connection to her past that allowed her to channel her anger into power. Even despite this limitation, Mukuro was still able to progress very far in the tournament, defeating S+ demons such as Natsume and eventually losing to the overall winner, Enki. It is very much certain that at her most powerful, there is only one character that would have any chance of defeating her. And that character would be…

Even though Raizen passes away during the series, the amount of reverence both his friends and his enemies have for him goes a long way in terms of how powerful Raizen is, as many state that he is the most powerful fighter. We get a sense of his power when he possesses Yusuke during his fight with Sensui to the point where he revives him from the dead, turns him into an S class demon, and channels his power through Yusuke in order to defeat Sensui once and for all. We first witness Raizen’s own demonstration of his power when his casual techniques are enough to effectively keep Yusuke at bay, far outclassing him. We also come to learn that in his prime, Raizen was so powerful that not even the combined effort of Mukuro, Yomi, and Raizen’s friends could stop him. It was only by his refusal to eat humans that his power weakens enough to the point where a stalemate was established between him, Mukuro, and Yomi. Throw in some flashbacks to Raizen in his prime effectively dominating his friends, and you have multiple examples of no one ever coming close to providing any kind of challenge for Raizen. In short, Raizen is without a doubt that most powerful character in YuYu Hakusho.