Since you're at the doctor's, medical headcanons. Who's afraid of needles, who's the biggest baby when sick, who insists that everyone just let them die, etc. etc.
Short answer before long one bc I have to drive but:
They're all deep, deep into the morass of the horrors and miracles of The Flesh.
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The Karakura kids are weird because Ichigo's dad is an emergency trauma doctor and Ichigo's family loves above the clinic. Any time his friends come over there's a round of "so what wild shit happened in the ER since last time?" Uryuu's dad is also a surgeon, and the thing that gets him and Ichigo back on speaking terms again is more or less second-hand shop talk. Orihime has been obsessed with emergency medicine since her brother died. She wanted to know what she should have done, and can do so it won't happen again. Keigo has been carrying a first aid kit in his backpack since he became friends with Ichigo and Tatsuki in middle school. He's got an exceptional talent for patching someone up enough to get through English class without the teacher noticing the injuries after a lunchtime brawl. Tatsuki started peeking over Orihime's shoulder at her notes on joint trauma and developed a talent for targeting her kicks and punches to deal maximum damage in karate tournaments. Mizurio knows a suspicious amount about neurology and how pain works because his "uncles" keep telling him about techniques used by enforcers to extract payment or information. Chad got heavily into Oxacan folk medicine because once he stopped getting in fights, he needed something else to occupy him, and his abuela decided to teach him how to cook. There is not a huge difference between good food and good medicine. He has an encyclopedic knowledge of chemoreactive plants and chemistry you can do on a stove.
Every single one of the Karakura kids has had something medical happen to them or a loved one, and every single one is now peering into the mysteries of the flesh about it.
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The shinigami are worse.
Shinigami broadly have better physical resistance, esp because they're reaping the injury stabilizing benefits Senjumaru wove into the Shinigami Shushako.
But they live in a feudal society that has only SOME of the benefits of modern medicine, and the few instances of disease-mitigating infrastructure are far between. It's COMMON for the souls of the rukongai and Seireitei alike to have a sibling who died in infancy or a parent who died in child birth or of an infection.
Societally, they are still in the very earliest phases of the war against pestilence and it gives one a very warped perspective on all things medical. Especially if you happen to be in the immediate sphere of influence of soul society's greatest warrior against death:
Retsu Unohana.
I cannot overstate the impact this woman has had, and you don't do things like "decimate the nationwide infant mortality rate" or "pioneer organ transplant surgery" without being a bit mad, and she has lived so long and done so much that the madness has clarified into a single extremely dense point of determination and she warps the reality of those around her. Woe and Blessings alike to those within her event horizon.
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The Arrancar are even worse.
Hollow resilience to injury allows them to body much, much worse injuries than the humans and it has an impact on etiquette. Biting off a hand because someone won't stop bothering you is a normal way to establish a boundary. Limb loss and regrowth is common, and disembowelment about as serious as a bad cold.
The food situation is even more dire. Smaller hollows, ones that used to be plants or animals or human-hollows who have a modicum of self control are weak, but lucky. They can survive off the ambient reiatsu in the atmosphere of Hueco Mundo, or the naturally cleaving fragments of soul that fall off the living.
Everyone else needs to hunt. And the more powerful a hollow becomes, the more it needs to consume, and the richer it's prey must be. The only really rich souls are other sapient beings. Any hollow at the level of Shrieker or Grand Fisher or higher is trapped in a hellish metabolic cycle of cannibalism, and the only way out is through.
The primary killer of hollows is other hollows. They know what they're doing. They're looking their fellow beings in the eye, the ones who understand them best, and deciding that their own life is worth their friend's. For all their ability to handle the slings and arrows of physical trauma, hollows are worse at handling the emotional consequences of this cycle. Monstrous Egotism is a best case scenario for them.
In practice, this means that while it's perfectly acceptable to bite someone's hand off for annoying you, it would be rude of you to spit it back at them. At least eat it!
I realize this last bit is not, strictly speaking, medical, but you can see how the ability to survive being turned into an anatomical Venus and having to live on a diet of the flesh of others would completely recontextualize how hollows think about Illness.
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I will do the fun individual headcanons when I get home, but this is a good broader framework to consider for now.
