I don't want to sound harsh.
We are OK with almost everything.
Integration is tough at first.
Feel at home, it won't take you long to integrate!

I allow myself to touch taboos for educational purposes.
(You cannot have people follow rules whose boundaries they don't know.)

Boards
Heyuri currently consists of boards as listed, no hidden boards to my knowledge.
Additionally you might want to check out these places:
1. UP - file upload boards, there is lots of old stuff and OC because they were not wiped unlike threads in Heyuri's earlier days. Though now Heyuri does not wipe old threads.
2. Wiki - free knowledge for learning what is Heyuri
3. CGI - it has chats and games, you can vote for next anime we watch or game we play, you can play with other heyurizens! (Heyurizen is a common name for people frequenting Heyuri)
4. Vote board, though I do not know its current location.

We periodically watch anime together. You will be notified as there will be an embedded announcement on /b/ with a timer.

Try using 'find' function in Heyuri wiki if you find something interesting. You can probably find it there at least in some capacity. If you are truly too lazy or there is no info on teh wiki you can ask it. I will respond to my ability.

Heyuri Associations
https://heyuri.net/index.php?p=links

Heyuri has an association with a video sharing platform.
Vidlii tried to carry spirit of old youtube.
https://www.vidlii.com/
Most Heyurizens use it. It is friendly or at least used to be friendly until morons swarmed to it posting hitler and calling everyone a nigger. Though it feels like a little village of friends to this day in a way, like Heyuri.
You can only realistically get warned for posting porn on Vidlii, or banned for posting porn constantly.
I think rules changed since then but that used to be the standard.
I can't think of another site that has this much of a userbase overlap as Vidlii.
There was an imageboard Nashi Kouen but it has died recently, spirit was similar but tamer.

Admins
The first admin of Heyuri was Lolico who tried to imitate old imageboard experience. He was doxed and left (I think). His avatar used to be Hatsune Miku, there is one emote of Lolico still in use.
It was taken over by Kuz who I think just liked to collect websites and some compared him to W.T. Snacks. Kolyma network fell. I wonder if Kuz was drafted by Russia. Kuz is gone. His avatar was Tomo from Azumanga.
Lastly and currently Heyuri was taken over by Kaguya as its third admin, Kaguya is involved in other sites but cares for this one very well. There is no admin besides Kaguya. His avatar is Kaguya from touhou.
A general rule is that if a tripfag has a colored tripcode - he most likely is a moderator.

Rules of Heyuri
Simple and can be found here:
https://www.heyuri.net/index.php?view=rules

Rule 0 - means you can't admit to being underage. That is because there were 3 lolis brough over from another site and one posted her room, things and later posted herself posing, finally she posted teh CP of herself (or so I believe) and this rule was added with all of them being banned and sadly parting ways, I still have most photos saved.
Rule 7 - means you are discouraged from discussing politics. It is a very low ragebait and leads to nothing. I think safe politics is politics that is irrelevant to modern day, so ridiculing irrelevant politics like discussing soviet union, yugoslavia or george bush for example; and related to them history seems fine to me. Besides we are too similar to have much differing political views anyway, what is the point of repeating things that everyone agrees on. (Personal opinion)
Rule 8 - this one prevents cancer and ensures cultural preservation. It used to be enforced hard but nowadays it is quite lax.