Nanashi's World, known unofficially as World B and the Secondary World, is an alternate world which runs in parallel to the primary world of the author and his three writing partners. It serves as the setting for Bleach: Tower of Night which featured Rōnin Shiba, the alternate counterpart to Kenji Hiroshi, as the primary character. It is also the world where Kentaro Shiba, Kaien Shiba, Fujimaru Kudō, Matsuri Kudō, Miyoko Kato and Shuji Kato originally hailed from.
Kaien, like his counterpart in the primary world, was a gifted prodigy who successfully entered the Shinō Academy on his first attempt. He and his cousin, Rōnin Shiba, shared a dream to become Shinigami, though Kaien's talents meant he achieved this long before Rōnin ever could. Kaien's natural genius and ability enabled him to graduate at the top of his class in only two years; he thus completed a six-year curriculum in one-third of the usual time, showcasing the depths of his talent. He subsequently joined the 13th Division under Captain Jūshiro Ukitake, and quickly rose through the ranks until he was appointed as Ukitake's Lieutenant.
Rōnin, however, was left to lament his inadequate skills compared to Kaien, leading Rōnin's father to ask him what he intended to do now. Rōnin, knowing he could not compete with Kaien in traditional fields, but still wishing to catch-up with his cousin, asked his father's permission to go on a pilgrimage throughout the vast Rukongai. Rōnin's father grants him his permission. Before Rōnin leaves his father and he play a game of chess, which his father wins. Rōnin travels to several shrines throughout Rukongai over a four-year period in hopes of studying both the Yuengiri philosophy and the Keidō martial art, which was the precursor to modern Kidō.
The twins Fujimaru Kudō and Matsuri Kudō, after being saved from Mad Eater by Seigen Suzunami and Kisuke Urahara and then healed by Konoka Suzunami, decide to become Shinigami to repay Seigen and Konoka for their kindness in taking them in. The pair graduated the Shinō Academy in six years and joined the 13th Division at Seigen's direction, for he wanted them to be free of the possible stigma that would have been attached to them had they joined the 5th Division, which Seigen was the Captain of. The pair worked closely with both Kaien and Rōnin.
Brother and sister duo Shuji Kato and Miyoko Kato escaped the slums of the outer Rukongai through differing means: Shuji enrolled in the Shinō Academy, where he demonstrated an innate predisposition towards Kidō, whilst Miyoko undertook tutelage under the Shunyōdō monks. After graduating Shuji enrolled in the Kidō Corps. Before Shuji left he fashioned earrings for himself and his sister; Shuji wore his from a chain, whilst Miyoko wore hers as an earring. Miyoko was left to hone her martial art skills in hopes of eventually catching up to her brother.
At the Shunyōdō temple, which was located within the twenty-seventh district of western Rukongai, Rōnin met fellow-student Miyoko Kato. Like him Miyoko wished to implement the older styles of combat with the new to catch up with someone close, in her case her older brother, who had already entered the Shinō Academy. The duo bonded over their shared goal and became close friends. One night Rōnin asked her about the earring she always wore. Miyoko explained that it was symbolic of a promise made between herself and her brother. Rōnin likened it to the dream he and Kaien once shared, and wished Miyoko well in her endeavour.
Rōnin, following his successful integration of both the Yuengiri philosophy and Keidō practices into a single art-form, returns to his home, where he speaks with Kūkaku and Ganju to get a general idea on how Kaien is doing and progressing. He is both shocked and delighted to learn of Kaien's swift ascent of the ranks within the 13th Division. Later that evening he is greeted by his father who makes note of Rōnin's inability to grasp the complex mechanics of letter-writing, with Rōnin remarking that it is good to see him well. His father asks after his progress, with Rōnin stating they can discuss it all over a drink and a game of chess. His father laughs upon hearing of his son's meeting with Miyoko and claims that he's a chip off the old block, and then asks if his son is ready to enter the Shinō Academy and begin closing the gap on Kaien. Rōnin claims he is. In response his father declares check-mate and implores his son to keep improving, and suggests they play again when he graduates. Shortly after Rōnin successfully passes the entrance exam and is placed within the advanced accelerated class based on his scores, where he once again meets Miyoko. Rōnin, like Kaien before him, proved himself a quick study, as did Miyoko. They imprinted themselves upon their Asauchi and achieved Shikai in only two years, and they graduated the academy itself in only three years. Rōnin's combat skills where particularly high, specifically in regards to Zanjutsu, which was the class he performed in with distinction. Upon graduation he and Miyoko said their goodbyes; Rōnin applied to join the 13th Division, whilst she applied to join the 10th Division.
The night Rōnin graduated he took his father up on his earlier offer and played him at chess, but was beaten once again. His father told him that he was not to rest on his laurels and continue to better himself as a member of the Gotei 13.
Kaien, acting on behalf of a bed-ridden Ukitake, assigns Fujimaru and Matsuri to patrol various districts of the Rukongai over the next few days, citing unusual Hollow activity. When Matsuri asks for additional information Kaien notes that the Hollow are beginning to act in coordinated groups and that this latest trend has the Captain's concerned. Fujimaru complains claiming that it will be trouble either way. Rōnin pokes fun at Fujimaru, saying he should have stayed in bed this morning, eliciting a yawn from the latter, who agrees. Matsuri quickly reprimands both for slacking off and assures Kaien that they'll get the job done. Fujimaru complains further, claiming no one will marry his sister with an attitude like that, which causes her to lash out at him.
In Rukongai Fujimaru and Matsuri rescue an Onmitsukidō operative from Hollow, who requests their assistance helping her rescue her Commander. She claims her Commander was injured shielding her from harm and that she was then sent away to get reinforcements. Fujimaru orders her back to the Seireitei to contact Lieutenant Kaien, claiming he will be able to help her. The twins arrive to see Yoruichi Shihōin, whose arm is hanging limp by her side, blocking a bridge off from a group of Hollow. She remarks that Suì-Fēng got aid to her more quickly than she expected and thanks the twins.
Meanwhile, at the Squad Station, Rōnin converses with Kaien regarding the Hollow's strange behaviour, and wonders if this has ever happened before. Kaien reveals that Captain Ukitake was apprehensive regarding the whole matter and implied that it has, indeed, happened in the past. At that point the pair receive an unexpected visit from Seigen Suzunami. The 5th Division Captain asks to see Fujimaru and Matsuri. Kaien tells him the duo are out on an assignment and aren't scheduled to be back until evening. Rōnin volunteers to bring a message to the pair but Seigen refuses, stating it can wait until later. Before Seigen leaves however he witnesses the arrival of an Onmitsukidō operative who asks to be taken to Kaien. Kaien asks her what the matter is. She explains the situation, relays her request for reinforcements, and further states that the Kudō twins of the 13th Division have already proceeded to the scene to assist. Kaien leaves the division in Rōnin's hands, claiming he will go personally, though Seigen claims that he has some free-time and will join him.
Yoruichi tells Fujimaru to be careful after the latter is almost cut down protecting her injured side. Matsuri asks if he is alright but Fujimaru tells her to focus on the foes before them, leading Yoruichi to remark that she likes the look in his eyes. She tells him not to hold back, leading Fujimaru to release his Zanpakutō into Shikai. Matsuri, exclaiming she won't be outdone, releases her own Zanpakutō. The twins proceed to re-engage the Hollow and progressively push them back but the arrival of a fresh group give the pair pause. Yoruichi then states it's about time. Seigen and Kaien arrive on-scene and release their Zanpakutō, with Seigen praising the twins for their actions. Yoruichi admits she wouldn't have made it without them. The five Shinigami fight back and defeat the group with the final Hollow remarking that "the Arrancar will destroy them all". Kaien asks what an Arrancar is but both Seigen and Yoruichi are stunned by its words and orders everyone back to the Seireitei, including the twins.
Upon their return Kaien takes Ukitake's place in a Captain's meeting when it becomes clear his condition hasn't improved enough for him to be up and about. Captain-Commander Garian Shinjo reveals what an Arrancar is: a Hollow who has evolved by removing its mask and gaining the powers of a Shinigami, shocking the assembled Captains. Thee only exception is Kisuke Urahara who keeps silent. Kaien then notes that the Hollow they dispatched claimed that this Arrancar would destroy them all, and asks how powerful they are. Garian claims an Arrancar's strength is based on the level of Hollow beforehand: an ordinary Hollow removing its mask would not be an issue for the Gotei 13, but a Hollow of Gillian-level or higher could be a considerable threat under the right circumstances. Shunsui Kyōraku notes that this could be problematic. Kaien goes on a gut-feeling and asks if it is possible for an Arrancar to exert some sort of influence over lesser Hollow. Garian admits that he does not know but notes that, if possible, it would explain the Hollow's sudden strange behaviour. He requests Captains Yoruichi, Kisuke and Seigen to remain behind, whilst dismissing the rest.
Calm Before the Storm
Captain Ukitake, maintaining that he is now well-enough to be active once more, comes across Kaien trying on one of his own Captain's haori when he returns to the Squad Station. Kaien apologizes though Ukitake says that it suits him and then asks for the latter's forgiveness for his extended absence, stating he appreciates Kaien's hard work. Kaien then asks for permission to promote Rōnin to the currently empty 4th Seated Officer's position, and further requests that the latter be made available to him as an aid. Given the circumstances Ukitake agrees. He then states that the Captain-Commander has asked the 13th Division to work closely with the 10th Division, given the recent loss of their Captain, to more effectively patrol the Rukongai. Ukitake further notes that the Kidō Corps are being scrambled as well and that Shuji Kato has been assigned to Kaien's command to facilitate easier communication. When Kaien asks what this means Ukitake tells Kaien that he has two hours to pick his patrol team.
Rōnin, Fujimaru and Matsuri discuss matters regarding the so-called Arrancar, with Rōnin passing it off as a bluff. Fujimaru admits that the situation has him worried though Matsuri assures him that the higher-ups will sort something out. At this Kaien interjects himself by stating they are the higher-ups response. He brings them up to speed and promptly adds all three to his patrol unit and then asks if they have any suggestions regarding further personnel. Matsuri, remembering Shuji from her own studies, claims that Miyoko Kato would make a good addition, with Fujimaru noting them to be siblings. Rōnin states that this would result in a tight-knit force even if he does dislike the Kidō Corps. Kaien tells his fellows that they have an hour to prepare and that he has to visit Miyoko. He requests that Matsuri accompany him and tells Fujimaru to sort things out for Matsuri, causing the former to huff, and asks Rōnin to sort his own equipment as well.
One month later Kaien and his team are the first to encounter a massive group of Hollow numbering in the hundreds. Fujimaru quickly admits that they can't deal with that many by themselves. Shuji claims he will contact the Seireitei using Kidō whilst advising a tactical retreat. Kaien reluctantly agrees and gives the order, though before they can do so the party are intercepted by a turquoise-haired figure, who claims all of them are his. He then states that he has little time to deal with lowly worms and proceeds to draw his sword, saying he will make this quick. Kaien and Rōnin join forces to intercept the figure's blade with Fujimaru lunging at him with his released Zanpakutō. The figure breaks the blade-lock with Kaien and Rōnin and moves to Fujimaru's back, claiming he is full of openings, and proceeds to attack. Fujimaru is shielded by a barrier summoned by Miyoko however and Matsuri uses this chance to release her Zanpakutō and uses Rengoku to attack from range, causing their foe to leap back. Shuji notes that his comrades bought him enough time and he obscures them all in a blinding flash of white-coloured light. When the light fades Shuji falls to his knees in exhaustion as Miyoko runs to his side, asking what he has done. Fujimaru notes they are no longer in the Rukongai. Shuji claims he transported the group to the Seireitei and advises Kaien to inform the Captains that the so-called Arrancar has finally made his appearance. Miyoko, however, sadly notes Shuji to have used forbidden Kidō. He claims he will happily answer for his crimes afterwards and again tells Kaien to go, with the latter telling Rōnin to come with him.
Garian calls an emergency Captain's meeting which Kaien and Rōnin attend, and they relate what they have discovered to the assembled Captains. Captain Ukitake asks for further detail regarding the so-called Arrancar's abilities. Rōnin claims he easily blocked their attacks, was fast enough to outstrip Fujimaru using Ryū Tenzoshu, and emerged from Matsuri's Rengoku without a scratch. Kaien further claims he would have killed them had it not been for Shuji. Captain Suzunami remarks that Shuji used forbidden Kidō. Garian, however, claims there was justification: without it the patrol team would have perished and the Captain's would know no more than they did before. He then orders the Gotei 13 to prepare for war. Outside Rōnin asks Ukitake what they are to do. He tells them to mobilize the patrol them Kaien had put together, noting he already received permission from the Captain-Commander, and tells Kaien to move to the front lines to intercept the Hollow.