Height
Of maturity and size.
Size barely matter in Gotei-13. Unohana knew and respected that some people who were considerably small were actually those who had an army of shinigamis under them.
It was more of a matter of wasting time rather than something important that Unohana could note how short Hitsugaya-taichou was. She couldn't blame him. He was the youngest--and the shortest--shinigami ever admitted as a captain. Shunsui-taichou had once joked if he could even reach puberty, at which Hitsugaya-taichou glared and ignored. And yet, he continued to be one of the most respected shinigamis in Gotei-13.
With Hitsugaya-taichou, it didn't really matter how small he was appearance wise. He was a wise captain with maturity that was a bit inappropriate to his size--and perhaps age--but was enough for him to be a captain. He was also as strong as the captains twice his height. The last time he and Ichimaru-taichou sparred--or were they trying to kill each other?--they both had ended up in her infirmary for days. Of course, sometimes Hitsugaya-taichou showed his child-like attitude when he asked her why Rangiku-san had had a weird thing on her front.
Soi-taichou was only half a head taller than Hitsugaya-taichou. Like him, it was no matter that anyone could press on. Soi-taichou could slice anyone calling her 'shorty' a few milliseconds after they said that. Anyway, she had proven herself to be more than capable of managing taller--albeit weaker--shinigamis. Unohana actually knew that her height was one of the factor that granted her the speed second only to Yoruichi.
Hinamori-fukutaichou could be doubted sometimes, what with her kindness and young age. Unohana herself admitted guilt of thinking that she had been a lucky hero-worshipping girl who managed to be a vice captain because Aizen-taichou was always there for her. She had to change her view and realized that it was no matter of age when she had witnessed her fighting many Hollows. After all, she couldn't get the position of vice captain in a young age without actually proving that she could.
But Kusajishi-fukutaichou...
"How did that happen, Madarame-san?"
"How should I know? One minute I was talking to Yumichika, the next minute she was sinking her teeth into my head!"
"I see. Had you used anything attractive to girls her age on your head?"
"No way. Those are for pansies...and Yumichika and Ukitake-taichou. Anyway, I used nothing! She thought I was a gigantic mantou or something..."
"Mantou?"
"Or maybe a candy."
Unohana stroke his shiny bald head to make sure that the medicine had been applied correctly. At least now Madarame-san didn't look as though someone was trying to lobotomize him.
"It's done. Shouldn't you tell Zaraki-taichou?"
Ikkaku snorted. "Yeah, right. He even told her not to do things half-heartedly, in other words he told her to sink her hungry teeth even deeper!"
The fourth division captain grimaced. "Oh, my..."
"Uh, huh. I think he's raising a second Zaraki Kenpachi or something...wait...that's creepy."
Unohana thought for a second. She went to her shelf and took one bottle, placing it in front of Madarame.
"Use this on your head everyday you thought she would jump on your head."
Ikkaku examined the bottle. Vaseline...? Oh, I see. Give her the bad taste, eh? I'll use it everyday then. Thank you, Unohana-taichou."
When Ikkaku left, Unohana couldn't help but remember that there were always exceptions everywhere. While the three aforementioned high ranked shinigamis could show their aptness in having that rank, sometimes she wondered if anyone had made the right choice when Kusajishi-fukutaichou had been appointed as a vice captain. Kusajishi-fukutaichou showed consistency in having a small child-like body and childishness.
Well, at least someone was enjoying their childhood.