In my own interpretation of the character of the Holy Roman Empire, he has an ethereal beauty or the kind of beauty that screams divinity or holiness. I depend on the Empire's historical connection with the Catholic religion rather than his comedic portrayal in Hetalia when it comes to his appearance and aura. I want the Holy or Sacrum part of the Empire to manifest in its personification. I read somewhere about Hima wanting Ancient Greece to give off the vibes of a goddess, which only increases my eagerness in portraying Holy Rome in quite a similar way. But his aura/appearance would not be compared to a god by his contemporaries, considering the prominent religion in his time and place was Catholicism and not a pagan religion anymore. I don't think he would like the comparison, either, because it implies he was being put on the same pedestal as God. Instead, he could be described as having an angelic/saintly aura and appearance, and he could make one think that he was a vicar of God or shouldn't be looked at or touched because he was just too sacred.
This, of course, also applies to him as a female, and this interpretation actually began when I was imagining a female version of him, which is, again, my preferred version. One of the reasons for that is connected to the headcanon above. Some qualities that come into my mind when thinking of someone with an angelic/divine/saintly aura and appearance are softness, gentleness, gracefulness, and pureness, which are traditionally associated with femininity.
