Northern Ireland was a part of Ireland which got annexed by the UnUK but recently reclaimed by Ireland in its new Monarcho-Fascist form. The culture of the area is quite diverse due to how often it has shifted hands and it is a rather rural area that still has many ethnic communities.
Many Irish people have settled into Irish communities and the Irish language and the cultural heritage of the area remain quite distinct from other parts of the area and the area also has a reputation for being quite friendly to immigrants. Northern Ireland has been a part of the UnUK for over 240 years but a large element of the Irish population remains in Northern Ireland.
Northern Ireland was annexed backed from the UnUK during the late 1300's to early 1400's during the later days of Saint Patrick’s rule. With that, the entire island of Ireland was now... well, all Ireland! And now, its new people were coming in to find better jobs (because they’re idiots, like, what kinda decent job can you get under a fricking Nazi ruling).
The new settlers were largely the same as those who made it the United Kingdom of Ireland. The Irish were mainly descendants of those who came over in the ships from the United Kingdom and the Irish were often those who were forced into the UnUK as slaves during the British era of slave trade.
Northern Ireland remains Ireland's “friendliest” region with less totalitarian interference with everyday life and such. It is less also religious/theocratic than the UnUK, but a good deal more religious than Norway - not much of a surprise when you think that Norway is a rather modern atheist society, but still.