I was just doing some research on eunuchs outside of my specific subject field – as one does – when I came upon the subject of Chinese court eunuchs. This got me thinking: despite a relatively close physical/cultural proximity with China, where there seems to have been a long (and consistent) history of eunuchs, I don't think I've ever heard of eunuchs in Japan.
So, I guess my question is actually twofold:
I was mostly wondering about eunuchs in court/imperial positions, but of course I'd be interested in any other information you might have! I don't know if I'm just missing something due to lack of context, or if there's a legitimate disconnect between the two cultures.
So the answer is a boring "no," which is not easy to expand on. But but buuuut... why there were no eunuchs in Japan (when there was in Korea and China) is really a bit of a head scratcher. Because there's enough social segregation with a highly complex social structure for them to seem "needed." (Per liminal theories of eunuchs, which I am assuming you know all about already so I will handwave over.) It's weird that they're not there, because on the surface they really should be.
The only comment on why this that I have ever seen is in the book Chinese Eunuchs by Taisuke Mitamura, which is an otherwise completely worthless book so I will save you from reading it. The author (who is Japanese) muses for a page on why there are no Japanese eunuchs, and puts out the idea that it is because Japan did not have any subjugated "other" group of people that it could pull eunuchs from. Which is a decent theory: societies generally have a distaste for castrating their own children, so when eunuchs get started up they almost always come from "others:" captured in war maybe, or just captured from other people, or sold children, or prisoners, or anything like that, just some group of people that it's okay to not think of as people. Many societies evolve into castrating their own children (like your Byzantines) when they get comfortable with eunuchs, but some never do (like the Ottomans). But it's hard to just wake up one day and say "let's castrate some of these little boys just lying here around being useless and make them politicians." It has to start from a place of subjugation and "otherness." So maybe that's why Japan just couldn't get it going, just not enough nearby subjugated people, even though they certainly had knowledge of the idea from China.