Almost as soon as Ichigo enters the Soul Society for the first time, he begins crossing swords with some incredibly powerful foes who push the courageous protagonist to his absolute limit, to the point where in some cases, he doesn't even win the fight.
Bleach has always been a shonen series notable for its fights, with manga artist Tite Kubo being able to depict battles in a fast-paced and intense style that many people compare to the legendary Dragon Ball Z, and these encounters are made all the more nail-biting when fans realize that Ichigo is facing someone much stronger than he is, resulting in a true battle to the death that is guaranteed to have any reader or viewer on the edge of their seat.
10 Renji
Despite being one of his closest allies later in the story, Renji Abarai is actually somewhat of an anti-hero during Ichigo's mission to save Rukia, believing that she must be punished for sharing her Shinigami powers, despite knowing deep down he doesn't want that to be the case.
This was the first time Ichigo faced a Vice Captain and the brutal fight that ensues tested everything he had learned up to that point, with Renji's destructive Zabimaru slicing through Ichigo's body and nearly leaving him for dead until he is able to concentrate his Spiritual Energy to finally take down the troubled Lieutenant.
9 Tsukishima
While Tsukishima is certainly no slouch when it comes to combat, it's really his psychological abilities before his battle with Ichigo that made him so threatening, with his Book of the End ability turning all of Ichigo's friends and loved ones against him.
This even leads to one of the saddest scenes in the entire series where fans see Ichigo break down crying on the floor upon realizing that Tsukishima had nearly stripped him of everything, including his new-found powers, that is until the Soul Reapers finally show up to save the day.
8 Ginjo
The deceiving and ever-mysterious Ginjo acts as Ichigo's ally for much of the Fullbring Arc, luring him into a false sense of security before finally turning on him in an attempt to absorb his powers for himself, but Ichigo is saved at the last moment by his Soul Reaper companions, who restore his lost powers, giving him a chance to fight back.
The fight pushes both men to their limits, with Ginjo desperately swinging his gigantic sword around to try and exterminate Ichigo for good, but once the Substitute Shinigami finally releases his Bankai, the fight is as good as over with Ichigo driving his Zanpakuto into Ginjo, defeating him once and for all.
7 Gin
While Gin had allied himself with Aizen, his true intentions were always hard to decipher, and what was even more unclear was how strong this former Captain of the Third Division was. Gin's Zanpakuto is incredibly small, so it seemed like he wouldn't be much of a threat to an Ichigo who, by that point, had become incredibly strong after his battles in Hueco Mundo, but once Gin unleashes his Bankai, which causes his sword to extend at a blistering speed, suddenly Ichigo realizes that he might have bitten off more than he can chew.
Luckily, Gin lets Ichigo live since he knows he's the only one capable of stopping Aizen, but there's no doubt he could have defeated him if he was truly intending to kill.
6 Grimmjow
The Sexta Espada, Grimmjow Jaegerjaquez, is often considered to be the closest thing to a rival Ichigo has ever had, with their second fight in Hueco Mundo often being cited as one of the best fights in all of Bleach, with it being a real test of endurance, strength, and speed for both combatants.
As Grimmjow gains the upper hand thanks to his Cero attacks and panther-like Resurreccion form, Ichigo must rely heavily on his Hollow Mask to give him even the slightest chance of defeating the Arrancar, which he eventually does after some verbal encouragement from Orihime.
5 Kenpachi
One of the bloodiest encounters in Bleach is during the Soul Society arc when Ichigo is hunted down by Kenpachi, the Captain of the Eleventh Division, who up to that point had been described as a bloodthirsty maniac who relies only on the sharpness of his blade to kill opponents, rather than ever using any abilities like Bankai.
Ichigo immediately knows he doesn't stand a chance as he runs around the battlefield for most of the fight just trying to stay alive, but as he throws himself into battle, suffering some life-threatening injuries while trying to defend himself, he realizes that he must unleash all of his Spiritual Pressure to cut through the captain's skin. Kenpachi forced Ichigo to become stronger in their fight and helped him understand his underlying power and how to direct it toward an enemy, while also teaching him more about the entity that lies within his sword.
4 Byakuya
Byakuya Kuchiki proved time and time again that he was not a man to be messed with as he casually left characters like Ganju and Renji lifeless without even unleashing his full power, so when Ichigo finally fought him, it was certain to be a dangerous undertaking, even with his newly acquired Bankai.
While surprising Byakuya with his lightning speed and powerful strikes, Ichigo is eventually bested by the Sixth Division Captain who devastates him with his Bankai, Senbonzakura, where his Zanpakuto disintegrates into a thousand tiny blade fragments that take the form of rose petals. The only reason Ichigo makes it out of this fight alive is due to his awakened Hollow Powers, which nearly take control of his entire body, resulting in a bloodbath that helped Ichigo develop his fighting style and abilities going forward.
3 Ulquiorra
Having defeated Grimmjow, who was the fourth-ranked Espada, Ichigo wasn't too worried about facing the Cuatro Espada, Ulquiorra, as soon as he was fully recovered from his injuries, but little did he know just how severely he had underestimated his latest enemy.
After Ichigo barely manages to keep up with Ulquiorra's speed and power after he unleashes his Resurreccion form, the Arrancar then unleashes his second form, which is much deadlier than the first. Ichigo not only loses to this form, but he actually dies in the process, with a gigantic hole now being implanted in his chest. Luckily, Ichigo's Hollow Form takes over his body, tearing Ulquiorra apart, but at the cost of Ichigo now being fearful of using his Hollow Powers ever again due to how violent they could be.
2 Aizen
By the time Aizen had merged himself with Hogyoku and was ready to begin harvesting the souls of Karakura Town, it seemed as if there was no one capable of beating him. After all, Gin, Isshin, and even Urahara had all tried and failed miserably, so to take him down for good, Ichigo had to make the ultimate sacrifice, and that was forfeiting his Shinigami powers.
This allowed Ichigo to reach his final form, which was capable of slicing apart mountain planes just by slashing his sword, but despite this incredible power, he still had to use his final ability, the Final Getsuga Tensho, to destroy Aizen, and even this didn't end up killing him since he was simply imprisoned after the battle finally ended.
1 Yhwach
By the last few chapters of the Bleach manga, Kubo had made the big baddie Yhwach so immensely powerful that there was virtually no way of overpowering him since he was able to overwrite his own death due to his ability to change the future.
Even with the help of Renji and the incredibly powerful Aizen, Yhwach was still able to shrug off attacks like they were nothing, proving that he had become an un-killable entity who Ichigo, despite being as powerful as he was by this point, still had no hope of defeating. It was only when Uryu used a Still Silver Arrow that halted Yhwach's powers temporarily so that Ichigo was finally able to hurt him, but this was clearly a plot device that had to be used to make the fight even remotely fair.