Gotei 13 vs. Kasumiōji Clan is an event which took place in Soul Society during the Kasumiōji Conspiracy. This event details the conflict between the Gotei 13 and the royal family, in which Yamamoto decrees that they are guilty of treason by creating the illegal Bakkōtō. Kumoi tries to ward the invading Shinigami off with his hordes of assassins, whilst Ichigo searches for the kidnapped Rurichiyo within the mansion.
Ichigo Kurosaki and 3rd Division Captain Shūsuke Amagai pursue the two Bakkōtō assassins who made off with Lady Rurichiyo Kasumiōji, with one of them facing off against Amagai, as Ichigo corners the other, leaving him out of options. He throws Rurichiyo into the air, attempting to use it as a diversion, but Amagai cuts him down. Ichigo rescues the princess, but realizes that it was a decoy. 
Rukia Kuchiki and Shū Kannogi come on to the scene, and they theorize that they were used as a decoy to mask the travel of the real princess. A Hell Butterfly approaches Amagai, informing him, urgently, to go to the stadium. As they arrive, Amagai wonders when Kibune joined the Kasumiōji Clan. He tells Aida and the others to take Lieutenant Izuru Kira to the 4th Division's barracks, as Ichigo asks him what's next. He tells the Substitute Shinigami that this is no longer a simple family feud. Suddenly, Lieutenant Renji Abarai appears in the training ground, and Amagai draws his sword, but Renji avidly claims that he is on Ichigo's side.
Rukia tells him what occurred at the training ground, as Amagai requests Renji to give 3rd Makoto Kibune's Bakkōtō to Yamamoto on his behalf, as he is going to infiltrate the Kasumiōji compound with Ichigo. The captain then theorizes that Rurichiyo is most likely there, as all of their safe houses have been discovered. Ichigo says they are counting on Renji, as Captain Jūshirō Ukitake tells his acting lieutenants to hold off on their orders. Yoruichi Shihōin approaches and tells him information. Renji forces himself into Yamamoto's office, Bakkōtō in hand, and places it on his table. Meanwhile, at the entrance to the Kasumiōji compound, Captain Tōshirō Hitsugaya and his subordinates stand guard, much to the contempt of Ichigo and Amagai. Hitsugaya calls out his name, as it is apparent he is aware of their presence. As Ichigo and the others try to plead their case with him, he refuses to listen, until Amagai steps forward, unsheathing his sword, clashing with Hitsugaya. He tells Ichigo to move ahead, as he uses Shunpo to evade the gate guards appearing upon the steps. However, Rangiku appears before them and Rukia decides to fight her, in order for Ichigo to move along.
As the fight between Amagai and Hitsugaya escalates, with both parties releasing their Shikai, Yamamoto declares that the Kasumiōji clan is guilty of treason, outlining that all members of the Gotei 13 are to break into the compound and gather all possible evidence. Meanwhile, Ichigo is seen following Shū's directions in order to find Rurichiyo. Yamamoto gives further instructions, stating that the 6th Division's Captain, Byakuya Kuchiki, to be in charge of the infiltration. The assassins report back to Gyōkaku Kumoi, stating that Yamamoto changed his original order, and that he has now ordered the Gotei 13 to invade the compound. .
Angered, Kumoi opens a cabinet filled to the brim with Bakkōtō, stating that he has no choice, but to use them. Rangiku is surprised that they have received new orders, and is relieved that she doesn't have to continue fighting Rukia. But their relief is short lived, as they are soon ambushed by a horde of assassins.
Rukia explains to Lieutenant Rangiku Matsumoto that they are assassins from the Kasumiōji clan, who wield katana known as Bakkōtō. Rukia and Rangiku are soon cornered back-to-back, surrounded by several of the assassins. Rangiku then releases her Shikai, sending the assassins sprawling onto the ground, before orange energy glows around them and they stand up to continue fighting, much to their surprise. Rangiku asks Rukia whether or not they experience pain, as the assassins converge upon her. However, Shūhei appears on the scene, knocking the assassins backward, informing them that the Kasumiōji Clan has been under suspicions for committing treason, and explains that they are to help Ichigo. The main force of Shinigami then enters the compound, successfully defeating all assassins in their path. Amagai is seen observing the Shinigami enter the compound with Hitsugaya, and are shortly accompanied by Byakuya, who informs them that he's been given the role of directing the infiltration.
Hitsugaya realizes the error of his ways, and promptly ends his fighting with Amagai. Amagai then leaves Hitsugaya's presence. Meanwhile, inside the compound, Ichigo and Shū are searching desperately to find Rurichiyo, but to no avail. They continue down a long hallway, before coming across a room filled with assassins, and Ichigo has no other option, but to fight them all. However, when he knocks them all down, they become possessed by their Bakkōtō and persist in fighting him, regardless of injuries sustained. Rukia arrives to assist him, using Kidō to defeat several of them. She explains that since Renji informed Yamamoto of the Kasumiōji Clan's treason, Kumoi has since been trying to cover his tracks. Ichigo tells Rukia to take Shū and go on ahead, in the logic that, since there are large numbers of assassins stationed here, there must be something important past this point. As Kenryū and Enryū are sitting in jail, they realize that something must be occurring, and Kenryū believes that Ichigo will rescue Rurichiyo amidst the chaos.
At the entrance to the compound, 3rd Seat Ikkaku Madarame and 5th Seat Yumichika Ayasegawa are seen warding off the assassins, only for them to revive themselves several moments later. Lieutenants Tetsuzaemon Iba and Shūhei Hisagi encounter the same problems, but state that the assassins could never hope to defeat them at their current level. Rangiku wonders what is going on; Hitsugaya informs her that it was all a part of Yamamoto's plan, in which they could not interfere with the operations of a noble family, unless it was for good reasons. Hitsugaya elaborates, saying that Yamamoto knew of the Kasumiōji clan's dark deeds all along, and used this situation as a means to infiltrate the compound.
Kumoi is seen being followed by two Bakkōtō-wielding assassins, and he is approached by another, who reports to him that the Shinigami have overtaken the main gate and pavilion, and will not be able to hold them off for long. He continues, saying he only needs time enough to enter the Bakkōtō smithy, but another assassin informs him that a Shinigami has entered the smithy. Kumoi dismisses this, saying it is impossible, as the barrier was erected by the Royal Family, and no mere Shinigami could break through it. The barrier around the smithy is seen crumbling, as the workers look on in surprise. The 13th Division members charge in, as Ukitake tells not a single person is to move. Despite this specific instruction, the workers start to retreat, before being blocked off by Kyōraku and his division members. Yoruichi commends an exhausted 2nd Division Captain Suì-Fēng upon breaking the barrier protecting the Bakkōtō smithy, and wonders who taught her such a powerful technique. Kumoi curses at the Shinigami's audacity, and tells the assassins to bring Rurichiyo to her, saying he has no choice, but to use her as a shield.
Despite Ichigo's desperate efforts to try and subdue the assassins, they persist, regardless of their injuries. He pleads them to stop, stating that they will perish if they keep this up. However, they refuse to listen, and he escapes through a window, closely pursued by the assassins. Rukia and Shū come across what seems to be a dead-end, but, upon closer examination, there is a floorboard out of place. Rukia opens it, to find Rurichiyo's two servants, who explain that she was taken away through a corridor in the room, which is a hidden pathway leading upstairs. Rukia and Shū proceed into the hallway, as Kumoi is berated by several other members of royalty, who explain that Shinigami have infiltrated the compound. They then tell him that they have knowledge of Kumoi's secret affairs, and the assassin puts Rurichiyo down on the ground. The group is surprised, and question what he is going to do with her, and Kumoi kills the leader of the group without hesitation. Kumoi then orders the other assassins to finish the rest off, as Rurichiyo questions the murder of her vassals. Kumoi tells her to be quiet, and throws her onto the floor unceremoniously. Rukia informs Ichigo that she is nearby, to which Ichigo glances upwards, and sees Kumoi making off with Rurichiyo with several assassins. He throws Rurichiyo onto the ground and tells her to be thankful he has kept her alive. She says she isn't thankful, as Kumoi points his sword at her, before being interrupted by Ichigo. Frustrated, Kumoi orders his assassins to subdue Ichigo, who knocks them out in one strike; their Bakkōtō clatter to the ground.
Ichigo points Zangetsu at Kumoi, telling him to hand Rurichiyo over, as Rukia and Shū appear. Kumoi points his blade at the princess, threatening to kill her if they move any closer. Rukia questions his motives behind the kidnapping, to which Rurichiyo says he wants to become the head of all nobility in Soul Society, through the use of the Bakkōtō. Ichigo says that he did all that to gain power, to which Kumoi says that he'll kill anyone who gets in his way. Ichigo says that what he has done is unforgivable, to which Kumoi says he doesn't need forgiving. Seeing that he isn't getting his message through, he presses his Bakkōtō's sword to Rurichiyo's neck, just as Amagai bursts into the room, much to their surprise. Kumoi is so shocked by Amagai's presence that he lets go of Rurichiyo, who runs towards Ichigo, but is stopped by Amagai's blade.
Kumoi sees an opportunity to grab Rurichiyo, but is dealt a fatal wound by Amagai, which kills him instantly, and he collapses before Ichigo and Rurichiyo. Rukia says that they'll never learn anything if the mastermind is killed, as Amagai sheathes his sword.
Amagai congratulates Ichigo on his work and picks up four nuclei from the Bakkōtō. He throws several sheets of paper into the air, illuminating the room in a green light as he makes off with Rurichiyo. 
- ↑ 1.0 1.1 1.2 Bleach anime, Episode 185
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Bleach anime, Episode 186