An official St. Patricks Day would work really well in Final Fantasy XIV lore. I can already think of how to implement it.

A Sharlayan NPC is mysteriously seen walking about Limsa Lominsa, and the adventurers are tasked with investigating the matter. It turns out that he seeks to bring tidings of Saint Coinach. A celebration about how the old Allagan Saint apparently drove the snakes out of ancient Alag.

The costume would be a leprechaun outfit, and you would get a wind up leprechaun.

What would you think. I know Little Ladies Day is a bit close to Saint Patricks aka what I would dub "Saint Coinachs Day", but it would be really fun.