As with any society or organisations, there will always be unspoken rules that you have to follow once you are part of it. Such a thing is inevitable, for it is human nature to abide by a certain framework that would construct some semblance of order. The presence of order is essential for everyone in the organisation to follow and reach a greater goal of making everyone's life easier as a collective whole.

The Soul Society is no different.

The Captains of the Gotei 13 are presences that command fear and respect in equal measures. However, there is a hierarchy even among the thirteen captains. Some captains held seniority over the others and the fact that they had lived and held onto their positions for so long was a statement of their power. The Captain Commander was one such individual, his students Kyoraku Shunsui and Ukitake Jushiro were also such individuals.

What most other people tend to forget were the pair of sisters who joined the Gotei 13 during the era where the Captain Commander Yamamoto founded the Gotei. Captain Unohana Retsu, the Captain of the Fourth Division had been around even before the Gotei was founded. However, very few had ever seen her draw her blade and those that did were mostly dead. The Fourth Division is also a division that rarely sees combat and as time passed, many shinigamis in the Gotei had forgotten that Captain Unohana Retsu had been around for far too long, and that there must be a much more sinister reason for her continued existence than just being merely good at Kaido.

Interestingly, when shinigamis speak of "Captain Unohana", the first person that they would think of was usually not Captain Unohana Retsu of the Fourth Division but rather, Captain Unohana Mihira of the Tenth Division. Captain Unohana Mihira is the younger sister of Captain Unohana Retsu. In contrast to how most shinigamis view Unohana Retsu, shinigamis were very well aware that Unohana Mihira was a very powerful shinigami who was so strong that the Captain Commander personally forbade her from ever invoking her zanpakuto's release command unless the situation required such an action. Not that Unohana Mihira really needed to rely on her zanpakuto; she was powerful enough to deal with most captains with just her hakuda alone and fight them to a standstill. Captain Zaraki could attest to that.

To quote Captain Zaraki: That bloody bitch just cannot die, but that's what makes fighting her so damn fun. Captain Zaraki's praise for Captain Unohana Mihira also aligned with the epithet that the Captain of the Tenth Division was rumoured to have earned in the wars that she participated in the era where the Gotei 13 was first founded, the Shitai Akuma (死体悪魔), which loosely translates to "dead body devil" or "corpse devil". According to the scant few rumours that still float around Captain Unohana Mihira was simply incapable of dying no matter how many wounds were inflicted on her and supposedly, that was how she earned her epithet.

Last but not least, there was one last rumour about the Unohana sisters, that there was an unspoken rule among the captains that Captain Unohana Retsu is to never head for the frontlines, and Captain Unohana Mihira is to never bleed. As to why and how this rule came into place, nobody knew for certain and no captain had given an answer when asked.

"So how much of those are true, captain?" Third Seat Hitsugaya Toshiro asked as he closed the latest issue of the Seireitei Communication Monthly, a magazine edited and published by the Ninth Division every month. This month's topic had briefly delved into the history of the organisation before expanding upon the rumours and myths about the Gotei 13 to generate interest in order to reach out to a wider audience. Among which, one of the rumours which the magazine had touched upon were the Unohana sisters.

"Oh? Which rumour?" Captain Unohana Mihira lazily opened her eyes from where she was lying on her reclining chair in the office to take a light snooze in this brief moment of respite. She slowly sat up and Hitsugaya respectfully handed a copy of the latest issue over to his captain, who quickly read through the contents that had intrigued her Third Seat.

"They aren't false," his captain admitted. "Shitai Akuma was my epithet back in those days. Ah, that's so long ago. Am I really that old?"

"So you can't die? Is that your zanpakuto's ability?"

"Far from it," his captain shook her head. "It's a technique I invented out of both boredom and necessity. Have you ever heard of the Second Division's secret technique that combines Kido and Hakuda, the Shunko?"

"A little in passing."

"My technique works similarly but for my case, I combined Kaido and Hakuda. Kido is a branch of offensive spells, but Kaido is a sub-branch that involves only healing spells. When you are able to utilise Kaido to the extreme and when combined with Hakuda, you can attain a body that can never die. That's the technique which I named Shitai, it allows me to not only reinforce and force my body to always be functioning at maximum capacity, it can also invoke instant regeneration that would heal my body before it could even bleed when damaged. This was the truth behind how I was given the epithet Shitai Akuma."

"Kaido? I wasn't aware that you can use Kaido, captain. Did Captain Unohana Retsu teach you Kaido?"

"It wasn't her. We both learnt Kaido under the same person," Mihira patiently explained. "Alright, that's not a story I wish to recount at the moment. I have already buried that part of my past behind, so let's not talk about it any further."

"M-My apologies, Captain."

"It's alright. Curiosity is a nice trait to have, but you also need to know when to stop digging before it gets dangerous. You never know when you would step on the tail of someone too powerful for you to deal with. Who's the editor of this issue anyway? He or she should have the decency to at least ask for my opinion before publishing such ancient history… Hisagi Shuhei? Why does that name ring a bell?"

Hitsugaya Toshiro watched as his captain slowly stood up, dusted herself, and exited her office with a warm smile that could disarm even the most vicious of men. He inwardly prayed for Hisagi's safety because he had, without a doubt, just earned his captain's ire for what he wrote in the latest publication.

There are many rumours and sayings within the Gotei 13 and he wouldn't know how many of those are true and false, but he could say with certainty that the rumour about both Captain Unohanas being scarily dangerous is definitely true.