No, NU isn't a clan. It's a Union. You have to be part of a clan in the NU like my clan. If you get in one of the clans in the union, your technically a member (or soldier, idk) of the NU.

You could join my clan by adding DC (which stands for Dragon Clan) in your narrow one game to be in my clan. you could also add it in your itch game if you want. 

and subbing to my chanel tooo would help.

https://www.youtube.com/channel/UCThevvwjlOi6AOsnqB9_DaQ 

yes you can

joining the NU means joining the clan alliance, but that doesn't put you in a NU clan. if you want to join a nu clan then you have to specify that you want to join.