The show's entire premise exists to watch you go from "this will be dumb" to laughing at how committed it is to the bit. Gender-swap comedy only lands when the character work is already there, and Hetalia's spent seasons building personalities so specific that seeing them rearranged just hits. This isn't fan service dressed up as a joke, it's the show trusting you already care enough about these characters to find the humor in a single, stupid, perfect premise.
The nation personifications of Hetalia take on a completely different form in this standalone special: they've been transformed into girls. What unfolds is pure comedic chaos as familiar characters navigate the world through an entirely new lens, their personalities and quirks intact but filtered through a gender-swap filter that creates endless opportunities for absurdity. The humor relies on watching how these character dynamics shift when you flip the script on who they are. Old rivalries take on new dimensions. Friendships develop unexpected angles. The show mines comedy from both the character interactions themselves and the inherent strangeness of seeing beloved figures reimagined this way. This is straightforward fun rather than deep storytelling. There's no grand plot driving things forward, just a parade of comedic moments built on the central conceit. It works best if you're already familiar with the original Hetalia cast and enjoy character-based humor that doesn't take itself seriously. The OVA knows exactly what it is: a playful what-if that exists purely to entertain rather than expand the lore.