Extra Vows 3
Section 7: Ōetsu Nimaiya
Ōetsu Nimaiya was the second person to ever become a member of the Royal Guard and has forgotten more about Zanpakutō than most will ever learn. Many hold his contribution to be even greater than Ichibē as while not everyone uses Kidō, all Shinigami use their Zanpakutō. Much like the earliest form of Kidō, Zanpakutō used to be created by instinct, with their wielder simply having so much power that a blade eventually manifested on its own. However, this also meant that only the strongest would have a Zanpakutō at all. That is, until Ōetsu discovered a foolproof method to draw out the Zanpakutō of any Shinigami. Unlike the earlier instinctive Zanpakutō, which manifested as distinct weapons, these newer versions would first start off as Asauchi, nameless blades with no distinct features or powers. A Shinigami would then infuse their Asauchi with their Reiryoku over time until they form their own unique Zanpakutō.
Ōetsu's own Zanpakutō mimics both his passion and his deadliness. The Sword Five that act as his assistants are in fact his Shikai, aiding him in his endeavors whether it be partying or forging new weapons. His Bankai is the incredibly simple yet absurdly deadly Sayafushi, a sword so sharp that it can't be sheathed.
As one who believes in the limitless potential of the Asauchi, Ōetsu holds a personal disdain for Ichibē forcing names, and thus limits, of his choosing on others.
Section 8: Senjumaru Shutara
The fourth Royal Guard ever appointed, Senjumaru was promoted for her creation of the Shihakusho. More than just a uniform, the Shihakusho is made from a special fabric that offers defensive power proportional to the Reiatsu of its wearer. Many a Shinigami lives have been saved by their uniforms absorbing sufficient damage to turn an otherwise lethal attack into a merely debilitating one. Upon being promoted, her ability with cloth increased to the point where she maintains a personal army of soldiers that are actually cloth golems. Within her palace, Senjumaru prefers to spend her days creating new fabrics and outfits only to give them away upon completion. Among the few exceptions is any clothing made from her special Ōken cloth, created from the bones and hair of the Royal Guard members. Though it has incredible defensive properties, being proportional to the Royal Guard themselves, those same properties make it worth no more than the standard Shihakusho to them.
While those who knew her before her promotion would recognize Senjumaru's artificial arms as her Shikai, her robe hides the true reason she keeps it active constantly. Not long before her promotion, a battle against the God King of Hueco Mundo cost her both of her arms. Sadly, not even Tenjirō, the greatest healer in Soul Society's history, could restore them. Unlike Shiba Kūkaku, who wears her disability with pride, Senjumaru carefully conceals her own out of bitterness.
Section 9: Tirana
The Hollow known simply as White had little in the way of personality or intellect, operating on a cold, ruthless instinct. Indeed, it was the years it spent inside first Masaki then later her son, Ichigo, which turned it into something more. Their thoughts, emotions, and experiences molded White until it became the woman who would name herself "tyrant." At her very core, Tirana can be best summarized as all of Ichigo's darkest thoughts and impulses, influenced by the remnants of his mother, and tainted by a Hollow's mind. She is his desire to dominate, destroy, and desecrate all wrapped into one undead woman.
Despite this, Tirana did hold some level of genuine, if twisted, affection for Ichigo. In her mind, she wasn't even lying when she made her offer to be gods together. While she would have been the absolute ruler of all, Ichigo would have been by her side as her loyal pet, which would put him infinitely above the insects she viewed everyone else as. His rejection destroyed any such fondness and now she desires to take his body for her own and rule as the God Empress she sees herself as. Fortunately, she's a coward at heart. So long as Ichigo is provably stronger than her, especially with Eien-ō always willing to aid him, she'll play the role of dutiful servant and let him use her powers as he sees fit. At least until an opportunity presents itself.
Section 10: Zanpakutō
Any Shinigami worth their salt knows that they need a certain amount of power to hear their Zanpakutō's name and thus learn its Shikai. Similarly, those who know the bare minimum of Bankai understand that it too has a minimum threshold of power to obtain and that a Shinigami has to best their Zanpakutō. Intellectually, they might even understand that their Zanpakutō spirit is born from their soul. But very few ever contemplate what this actually means, and most who do are among the strongest Shinigami in Soul Society. A Zanpakutō spirit isn't merely born from their wielder, it is their wielder. Or rather, a portion of them, often one they do not acknowledge. As such, a Shinigami who complains about a lazy Zanpakutō will rarely notice their own laziness.
Currently, there are only five Shinigami to have gained their Zanpakutō without undergoing the standard ritual to pull it from their soul (Not counting Kurosaki Ichigo, whom everyone agrees should have an asterisk next to any exceptions including him). Both Yamamoto and Retsu obtained their own Zanpakutō long before the ritual was created by Ōetsu. Zaraki and Yachiru both created theirs on accident from the raw Reiatsu they exert. And finally, and most curiously, Tosen Kaname took the Zanpakutō of his fallen friend and made it his own, a feat which earned his Zanpakutō the unique status of having two Shikai. If anyone ever asked him, Ōetsu would explain it was only possible due to the fallen Shinigami having not fully attuned her Zanpakutō before she died and that Tosen's own sound-based Zanpakutō corrupted the original Shikai ability of the blade duplicating itself.
There's a saying among the most learned in regard to Zanpakutō: Shikai is what you present as, Bankai is what you are. That is to say, your true character is presented in your Bankai. Two particular examples would be the late Kurotsuchi Mayuri and 7th Division Captain Komamura Sajin. The former's Shikai is much like his outward demeanor: Somewhat distasteful but clearly useful. However, his Bankai is as monstrous and toxic as the man himself. By contrast, the latter's Shikai portrays him as a mighty warrior and guardian and his Bankai is simply more of the same, showing he truly is what he presents himself as.
Learning the name of one's Zanpakutō is merely the very first step towards acknowledging all of oneself. Similarly, the process of obtaining Bankai is less about the actual physical conflict with one's Zanpakutō spirit and more about acknowledging and accepting all of oneself. There's an often discussed and equally often dismissed rumor of a further level beyond even Bankai though few can even guess what such a power might entail or how it might be acquired. Outside of the Royal Guard, only one can say with absolute certainty. Yoruichi still misses her Zanpakutō.