Bleach is a long-running animated series that is broken up into several major story arcs, and the Soul Society arc is easily one of the most exciting, creative, and consequential story arcs in the entire story. It began when Ichigo and his friends snuck into the Soul Society to rescue Rukia Kuchiki, who had been sentenced to an unfair and cruel execution. Many thrilling battle scenes ensued.
By the end, it became clear that Captain Sosuke Aizen was the mastermind behind all this, and that was when the Soul Reapers called a truce with Ichigo's team to face this threat together. So, at this point in the story, who were the most powerful characters who had appeared? Many of these powerhouse characters would go on to be major players in the next arc, too.
10 Captain Mayuri Kurotsuchi
Captain Kurotsuchi is the mad scientist of the Gotei 13, and he would later fight his Espada equal, Szayelaporro Grantz. And during the Soul Society arc, he proved himself a creative but deeply cruel researcher who liked to experiment on himself and others alike.
With his zanpakuto, his experimental drugs, special devices, and more, he could disable or trap any opponent, and he could attack his enemies with a stunning variety of techniques. His giant bankai, Konjiki Ashisogi Jizo, could emit poison gas that could swiftly kill a target.
9 Captain Soi Fon
The boss of squad 2 is Captain Soi Fon, who is a trained ninja and assassin. She can covertly sneak in and out of any base or battlefield, and once the fighting starts, she can use expert-level martial arts, kido, and shunko (a kido/martial arts combo) to take down her foes.
If that weren't enough, Soi Fon could use her shikai, Suzumebachi, to sting an enemy twice in the same spot and kill them. No one can survive such a sting attack. Not even her mentor, Yoruichi Shihoin, can use an ability like that.
8 Captain Toshiro Hitsugaya
Many of the most powerful characters in the story are Captains since a Captain is the most elite rank. Squad 10's leader is Toshiro Hitsugaya, who is by far the youngest Captain, and he is a veritable child prodigy on top of that.
Already, he is a master of the sword, and his ice-based shikai and bankai are devastating. Toshiro is still growing in skill and technique, and as of the Soul Society arc, he could break even with Gin Ichimaru, another swordmaster.
7 Kisuke Urahara
Kisuke Urahara is more than a candy shop owner; he is also an ex-Captain, meaning he has strength, speed, and sword skills to match most current Captains. His shikai can release a powerful blast of red energy on command, too.
Besides, Kisuke is an expert scientist, allowing him to read his opponent's techniques and assess them to figure out their weaknesses. Finally, Kisuke is a powerful caster of kido spells, even though he's not a part of the Kido Corps.
6 Yoruichi Shihoin
Here is the woman who taught Soi Fon the way of the assassin: Yoruichi Shihoin. She first appeared before Ichigo as a black cat, but she is actually an ex-Captain, and no one can move quicker than her. Her flash step has earned her the nickname "Goddess of Flash."
As her student, Yoruichi is a master at assassination, stealth, and martial arts, and she can use her bare hands and feet to beat an opponent senseless. And it was she who invented shunko, wrapping her body in electric kido to augment her physical prowess even further.
5 Captain Kenpachi Zaraki
At this point in the story, Kenpachi Zaraki had proven himself quite powerful, but he hadn't yet reached his full potential. By the Soul Society arc's end, Kenpachi was not yet capable of performing shikai or bankai, nor did he know his zanpakuto's name (he later learned that it's Nozarashi).
The scary thing is even with just his sealed zanpakuto, Kenpachi was a true monster on the battlefield, using his incredible strength and endurance to fight opponents' blade to blade and overwhelm them. It was lucky that Ichigo survived their fight at all.
4 Captain Byakuya Kuchiki
The squad 6 is the aristocratic Captain Byakuya Kuchiki, Rukia's adoptive brother, and the head of the noble Kuchiki family. His flash step is famously quick, though he's not quite as fast as Yoruichi is. Still, he has a lot going for him.
Byakuya combines that speed with expert swordplay, and he can use advanced kido spells and his shikai, which attacks the enemy with hundreds of petal-like blades. If that's not sufficient, he can use bankai, Senbonzakura Kageyoshi, to obliterate his enemy with millions of such blades. Not even Espadas can survive those attacks.
3 Ichigo Kurosaki
Ichigo Kurosaki, the hero, only barely has the edge on Byakuya, since he lacks kido spells and hasn't been fighting for nearly as long. But still, his inner Hollow power had begun to manifest by now, and it made him incredibly powerful, even if he couldn't control that power too well.
Besides, Ichigo had incredible guts, unorthodox fighting styles that took his enemies by surprise, a fast and sharp bankai, and the Getsuga Tensho on top of everything else. It was he who took on Renji, Byakuya, and Kenpachi and won.
2 Captain Sosuke Aizen
Here is the villain himself: Captain Sosuke Aizen. He had enormous power, even compared to other Captains, and he needed minimal effort to defeat an exhausted Ichigo when they clashed. First, he is a master of the sword, and his spiritual pressure is overwhelming, even compared to Byakuya's.
Aizen is also highly proficient in the use of advanced kido spells, and most of all, his shikai, Kyoka Suigetsu, can trap its enemies in perfect hypnosis or illusions. With powers like those, Aizen can take on nearly any foe and win, and that's before he gained the power of the Hogyoku.
1 Captain-General Yamamoto
This wise older man is nothing less than the commander of all Soul Reapers, and he has combat power to match. His best years are behind him, but even then, his sheer strength is unlike anything else the Soul Society has ever seen.
With just his shikai, he can take on Shunsui Kyoraku and Jushiro Ukitake (though they barely appeared in the Soul Society arc, so they're not counted here). His spiritual pressure and energy are like a looming mountain, and his shikai and bankai are enough to burn any foe to ashes with impunity.