After doing some brief Wikipedia research it looks like *O'* indicates “descendant of” while *Mac* indicates “Son of”. In Gaeilge, the Irish language, these names are written as Ó (Name of Ancestor/Father). For Example, O'Reilly becomes Ó Raghallaigh, which means "descendant of Raghallach".

Interestingly, Gaeilge has a difference in surnames for women and men, which was not carried over in the Anglicization of Irish surnames. The Ó and Mac becomes Ní and Nic respectively. These literally mean "descendant's daughter" and "son's daughter". This would mean that my surname in Gaeilge would be Ní Raghallaigh, which doesn't have a direct anglicized version.

Another fascinating piece comes from when a woman is married and takes on the name of her spouse. Still using O'Reilly as an example, an Irish woman taking on the name of Ó Raghallaigh would write it as Bean Uí Raghallaigh, which can be shortened to Uí Raghallaigh. Bean Uí Raghallaigh translates to Wife of the Descendant of Raghallach(bean = woman, uí = descendant). For example, My name(Kiera) in Irish if my surname was derived through marriage would be Ciara Bean Uí Raghallaigh, literally "Kiera, the woman related to the Descendant of Raghallach". After English Anglicization, This becomes simply Kiera O'Reilly(or Kiera Reilly depending on if the O was removed in Anglicization) because the gender and relationship based language was lost in translation.

If I'm understanding correctly, Uí is not gender specific for the person it is referring to, and instead is just a version of "descendant" which indicates a relationship between the main subject, the descendant, an the ancestor. This takes the form of [Subject i.e Bean(woman)] + [Descendant i.e. Uí] + [Ancestor i.e. Raghallach]. Together this is Bean Uí Raghallaigh as the full surname.

With this interpretation, a woman married to another woman would still use Uí, for the same surname of Bean Uí Raghallaigh.

If a man were to take on another's surname in marriage we can hypothetically use the same rules to figure out his new surname. Since "Fear" means man, we can replace the word for woman in the surname. For example, a man named Connor (Irish Conchobar) with the married last name O'Reilly would become Conchobar Fear Uí Raghallaigh. This is not necessarily an official rule of the language due to the historic lack of legally recognized gay couples and the changes in culture since the modern form of Irish evolved. I think this would work well in this use case however.

This'll be a 20 x 27.5 cm (7.9 x 10.8 inch) print that I'll hopefully be able to work on this week (thank my art teacher for giving me a lot of rubber to work with over the summer)

I'm kinda iffy with the design of rogier's sleeves because it makes it look like its made out of thick material. The bottom right part is also too messy rn and I'm not very happy with the flow and shape design of the deathblight but lmk what u guys think