After Ichigo successfully blocks the Sōkyoku's attack on Rukia Kuchiki, the Sōkyoku is destroyed by Captains Shunsui Kyōraku and Jūshirō Ukitake. Breaking the Sōkyoku's stand, Ichigo throws Rukia to Lieutenant Renji Abarai, who runs away with her in his arms.
Lieutenants Marechiyo Ōmaeda, Chōjirō Sasakibe, and Isane Kotetsu are sent to chase Renji, but Ichigo, blocking their path, effortlessly defeats all three without the use of his Zanpakutō. Picking up his sword to defend himself against Byakuya's first attack, he tells Byakuya he can see his every move.
As they cross swords, Byakuya asks Ichigo why he keeps trying to save Rukia, but Ichigo asks why Byakuya is not trying to save her. Brushing it off as a pointless question, Byakuya states even if he was inclined to answer, Ichigo would not understand. After the two clash and push themselves apart, Byakuya tells Ichigo he will kill him and carry out Rukia's execution with his own hands, but Ichigo states this will not happen. The two charge at each other.
The two continue to battle one another fiercely, causing explosions all around Sōkyoku Hill but each of them continues to block and effectively parry the swings of the other over and over again. With neither of them able to gain an inch, both back away from one another and Byakuya commends Ichigo for mastering Shunpo so quickly. Byakuya goes to state that Ichigo will still lose the battle but the boisterous teenager interrupts him mid-sentence and asserts that Byakuya is going easy on him. Reminding the captain that he intended to kill Ichigo and that he is still uninjured, Ichigo taunts Byakuya while smirking, trying to get him to use his Bankai.
Ichigo reminds him of his promise to kill Rukia, his own sister but Byakuya asks why he has a problem with his words. Ichigo states that he detests those words and that he intends to use all his strength to defeat Byakuya. He also insists that, no matter the circumstances, after his victory, Byakuya will never speak such words in front of Rukia again and then he will force Byakuya to apologize to her. Byakuya sees through the taunt and chastises Ichigo for his insolence, stating that he hasn't changed his mind about Ichigo nor Rukia's fate. He refuses to use his Bankai, believing Ichigo to be unworthy of its power. Instead, Byakuya releases his Shikai, Senbonzakura.
Byakuya's Zanpakutō begins to disintegrate into thousands of tiny blades that spin towards Ichigo in order to attack the teen. Despite this, Ichigo appears calm before he lifts his blade and swings it towards the oncoming attack, unleashing a massive, blasting stream of blue Reiatsu that shocks Byakuya with its power. When the dust clears, Byakuya's glove falls from his left hand to the ground and blood begins to drip down as the captain demands to know what that attack was. Ichigo explains that his Zanpakutō gathers his Reiatsu and releases it in an amplified swing in an attack called Getsuga Tenshō, which Zangetsu had just revealed to him.
Ichigo thrusts his blade into the ground and again demands that Byakuya attack with his Bankai as he intends to destroy the captain completely. Byakuya mocks the name of Getsuga Tenshō as pretentious but decides to give Ichigo what he wants and releases his Bankai; Senbonzakura Kageyoshi. Ichigo is stunned when his opponent drops his blade into the ground before tens of blades rise up around him. They all scatter in many more, countless, much smaller blades and go to attack the redhead. Ichigo manages to avoid the blades several times but Byakuya indicates that this is useless, even when Ichigo unleashes another Getsuga Tenshō that Byakuya easily blocks.
Many of the small, densely populated blades swarm behind Ichigo, taking advantage of his distraction. Ichigo turns just in time to try and block the attack but he is soon overwhelmed by the sheer numbers of the tiny blades and is slammed into the ground as Byakuya looks on. Byakuya compliments Ichigo's abilities but states that his attacks are far too slow to evade the nimble assault of his innumerable blades. Injured along his arms and forehead, Ichigo states that he thought he could beat the Bankai but he failed. He goes on to state that this is a logical outcome since he was still only using his Shikai to battle it and underestimated Byakuya in doing so.
In reaction to his words, Byakuya insults Ichigo for his perceived arrogance and warns him to be careful with how he speaks as he is trying to suggest that he has already achieved Bankai himself. In response, Ichigo smirks as he asserts that he is implying exactly that. Byakuya is disbelieving of this so Ichigo insists that he will see it with his own eyes and begins to gather his Reiatsu. Byakuya is mesmerized, by the thought that someone who is not a noble and was not even born a Shinigami can talk of Bankai, the ultimate Zanpakutō technique, with such ease while emitting such a vastly dense Reiatsu. Awestruck, he watches as Ichigo releases his Bankai; Tensa Zangetsu.
When Byakuya looks over Ichigo's new blade, seeing that it is very small compared to his Shikai, asks if that is not just the normal, sealed stated of Ichigo's Zanpakutō. Believing this to be true and that Ichigo is mocking him, Byakuya summons his many blades and decides to carve into Ichigo the penalty for stepping on the pride of the Shinigami. However, despite the fact that his blades are in front of his, Ichigo manages to suddenly appear close enough to Byakuya to point the tip of his blade to Byakuya's neck, stunning the veteran Shinigami. Ichigo asks if their pride has anything to do with Rukia's execution since, if it was, then he would gladly step on it.
When Ichigo pulls away, Byakuya reflects that for an instant, he lost sight of of his opponent, something that greatly confuses the captain. Stubbornly refusing to accept that Ichigo has achieved Bankai, Byakuya asks why Ichigo pulled away without killing him, surmising that arrogance destroys the footholds of victory. He declares that Ichigo does not have Bankai, once again readying his blades to attack while advising Ichigo that he will soon regret not slicing his throat open when he had the chance as miracles do not happen more than once. He sends his innumerable blades towards Ichigo and the teenager effortlessly evades them multiple times.
Confused, Byakuya wonders why Ichigo can move so fast as his Senbonzakura Kageyoshi cannot keep up with him. Ichigo begins to show some of the speeds he can achieve while taunting Byakuya that he can move faster if he wants to. In response to his cockiness, Byakuya begins to use his hands to move his blades stating that, in doing so, he's twice as fast and that there is nothing he cannot catch. Just as his blades completely surround Ichigo, the captain believes he has caught the Shinigami but instead, his opponent begins to swing his blade at unimaginable speeds, slicing through and deflecting them all.
Byakuya watches wide-eyed, disbelieving that Ichigo was able to easily deflect every single one of his blades. Ichigo appears behind him then, wondering about his words about miracles only happening once, then what would Byakuya call this and moves to stab the captain. Byakuya barely manages to avoid the mortal blow but is forced to redirect Ichigo's powerful with with his bare hand, causing it to bleed profusely. Byakuya manages to deduce exactly what Ichigo's powers are; he is able to take the sheer power of Bankai and condense it into a small blade that allows him to fight at hyper speeds. Complimenting the power of his Zanpakutō Byakuya yells angrily that he must now eradicate that power.
As Byakuya grips Ichigo's blade with his wounded and bloody right hand, both of them stare at each other for a tense moment. He lowers the blade and both combatants jump backwards, away from each other in apprehension. Byakuya decides to end the battle by introducing Ichigo to what he calls Senbonzakura Kageyoshi's "True Form". The millions of tiny blades disappear and unite to forms thousands of glowing swords that begin to float around both Ichigo and Byakuya in four circular rows. The captain states that this form of his Bankai abandons all defense and focuses everything on killing his enemy.
Ichigo stands awed by the sight and Byakuya mockingly reassures Ichigo that the thousands of blades will not attack him all at once. Byakuya reveals that he made a vow that this form of his Bankai would only be shown to an enemy he deems worthy to be personally killed by his hands; Ichigo is only the second person to see this technique. Recovered from his shock, Ichigo smiles and thanks Byakuya for what he considers to be a compliment. Byakuya allows one of the glowing blades to drop as he catches it and the two of them begin to battle again, resulting in a massive explosion that shakes the area around them.
As the two continue their fierce clash neither manages to draw blood on the other as they exchange blows time and again but nobody manages to wound the other. After several more attacks and parries of attacks, both of them push apparent to observe their opponent. Ichigo is now panting heavily, reflecting that Byakuya is now able to fight at a higher speed and he thinks that this is due to his Senkei ability and ever since, he has been getting faster and faster, time and again. However, Ichigo decides that this isn't a problem as he knows that he can also move at faster speeds if he chooses to.
Suddenly, while Ichigo is lost in thought and before he increases his speed, the tip of Byakuya's blade appears in front of Ichigo's eyes in an attempt to kill him. Ichigo manages to evade a fatal blow with his speed, but the captain manages to slice his blade along his right cheek despite this, cutting deeply. While the teenager is distracted by the blow, Byakuya appears behind him, taking advantage of his distraction in order to attack. Despite this, Ichigo manages to just evade the blow to his neck and clash blades with the captain once more, both of them pushing against one another in a stand off.
As they continue to push their blades against one another, Byakuya sardonically asks the teenager what is wrong as he deduces that his movement have become sluggish. In response to the taught, Ichigo smirks while maintaining that Byakuya's blade has been moving so slow it might as well not be moving at all. Ichigo's flat rejection of the reality of the situation causes Byakuya to react in kind, summoning another one of his swords from the area surrounding them and stabbing the teenager in his right foot, causing him a lot of pain and shock at the surprise attack.
Immediately following up on his new advantage, Byakuya points to Ichigo's right shoulder and blows a hole through it using Hadō.#4 Byakurai. He then removes the blade from Ichigo's foot as the teenager stumbles to the ground due to his injury, landing on his knees, doubled over. Byakuya asserts that Ichigo is at his limit while the teen realizes that he cannot move due to his injuries. The captain explains that Senkei only increases the the level of his attack power but does not increase his speed and thus Ichigo sees that he was the one who got slower. Byakuya compliments Ichigo on making it this far, defeating so many enemies in the process but now, it is the end of the line for him as his body has reached its limit.
Deciding to end the battle, Byakuya summons another blade and raises it above his head in order to kill Ichigo once and for all. Stunned by this turn of events, the teen mentally struggles with the reality of his predicament, willing his unresponsive body to move. He reflects that he came to the Soul Society to win, not to just fight and not to merely survive but to win. His desperation fades as his hand suddenly shoots out and catches Byakuya's blade before it connects. Ichigo's voice becomes warped as a new persona, Zangetsu, takes over his body and declares that dying would be a problem for both of them. Watching as a mask begins to form on the teen's face, a shocked Byakuya demands to know the name of the being who has taken over Ichigo, but Zangetsu denies his request, stating that he does not have a name.
After declaring that he has no name, much to Byakuya's surprise, Zangetsu takes over the battle and speedily slashes the Shinigami across the chest, creating a deep wound, knocking the captain backwards, before slicing again forwards at the air while laughing maniacally. Byakuya is stunned by the sudden turn of events, and watches as Ichigo appears to be speaking to himself. The Hollow, now in control, criticizes Ichigo's awareness, calling him an amateur as he hasn't noticed that due to his inexperience, his Bankai has been crushing his bones and causing them to creak since he activated it. Zangetsu then determines that he will show Ichigo how to properly use his Bankai. Byakuya swiftly collects another blade and is shocked to find that Ichigo is now attacking with a black Getsuga Tenshō.
As Byakuya moves to evade the attack, he notices that Ichigo has moved on the offensive to his left. Subsequently he expertly and speedily uses Shunpo to evade that attack as well. However, much to his utter astonishment, he backs into Ichigo's palm, finally realizing, too late, that his opponent has undergone a massive increase in both speed and power. Ichigo then slashes Byakuya, destroying the surrounding field created by his Senkei ability and smashing the kenseikan from the top of his head which also has been wounded and begun to bleed profusely.
Recognizing the kind of Reiatsu that Ichigo is now exhibiting and the type of mask forming on his face, an exasperated Byakuya demands to know if Ichigo is a Hollow. Zangetsu replies with a mocking tone, before stating that Byakuya shouldn't care as he doesn't need to know given that he is about the finish the battle. However, before he can finish his threat, Ichigo begins to regain control of his body, telling Zangetsu to leave the battle. The red-haired Shinigami manages to grab the mask and a struggle between the two personalities begins to ensue as Zangetsu declares that he can defeat their enemy, but Ichigo wants to fight with his own strength and rips the mask from his face as Zangetsu screams in a seeming mixture of pain and frustration.
Back in control of his own body, Ichigo pants heavily as the mask crumbles around him. Byakuya watches on, stunned, as Ichigo expels a heavy sigh before he apologizes for his inner Hollow interrupting their battle. Perturbed by Ichigo's nonchalance regarding what happened, Byakuya realizes that Ichigo wants to defeat him without the aid of the powers he just witnessed. Byakuya agrees to disregard what had just happened whilst asserting that neither of them have the strength to battle for much longer and this will be their last blow. He agrees that if Ichigo wins, he will explain why he hasn't tried to save Rukia. With that, Byakuya gathers his remaining Reiatsu and activates his Shūkei: Hakuteiken ability.
Amazed by the brilliant white wings of Byakuya's new ability, Ichigo compliments him on it. Ichigo goes on to apologize because he does not have anything as fancy as Byakuya's various abilities as Zangetsu only taught him the Getsuga Tenshō. Despite this, he resolves to put everything he has left into this final attack. He begins to summon and compress his remainder Reiatsu until he is covered in a circular, black aura that contrasts strongly with the white light of Byakuya's appearance. Calling out his adversary's name, Ichigo charges at Byakuya as the noble also does the same, creating a massive explosion of Reiatsu that engulfs the entirety of Sōkyoku Hill.
The effects of the clash is felt across the Seireitei in a colossal blast that other Shinigami feel. As the dust clears, both combatants are standing apart with their backs to one another. After a pause, blood explodes from Ichigo's back and shoulder and he pushes his bladed into the ground for support, refusing to fall after coming so far. Byakuya finally shifts and blood also explodes from a deep wound across his chest, causing the captain to stagger forward several steps. He reflects that during their clash, Ichigo's blade shattered his own and stares at the remnants of his Zanpakutō left in his hand as they flutter away in the wind.
Clenching his fist, Byakuya decides to alert Ichigo to his reasons for supporting Rukia's death. He reveals that as both a member of the Gotei 13 and the head of the Kuchiki Clan, a great Noble House, he is obligated to act as a an example of how the law should be obeyed, for those below him to follow, regardless of family ties. Ichigo understands but states that in Byakuya's position, he would use all his strength to fight the law to protect his sister. Byakuya is reminded on Kaien Shiba and realizes that Ichigo is just as liberal as the former Head of the Shiba Clan in that the current laws were Ichigo's true enemies, not Byakuya himself.
Byakuya informs Ichigo that his recklessness has broken his blade that thus he cannot continue the battle, nor pursue Rukia any longer and thus Ichigo is the victor. With that, the greatly wounded captain uses Shunpo and abandons the battleground, leaving Ichigo alone on Sōkyoku Hill. The red head stands stunned by the news of his victory before dropping his sword and crying out loudly in jubilation of his triumph. However, he soon becomes lightheaded due to exhaustion and falls backwards only to hit the back of his head against Orihime's forehead after she arrives and tries to help him. Ichigo is happy to learn that his friends are alright and Orihime tearfully thanks Ichigo for surviving his battle with Byakuya. Ichigo stares at her before thanking her for her concern and support.