Wow! How very fun. I love HP in Egypt stories, but apart from this brilliant new fic of yours, and Josan's "Once Upon a Time in Egypt," I can think of none that so beautifully transport the reader to this distant time and different way of life, while still keeping our favorite characters recognizable.
Your research shines through in all the right ways (which most people writing historical genres fail to master). The easy, wrong way is to stuff all manner of research notes and factoids into the text, thus turning it into an impressive but lifeless, overloaded museum display. But you did it *so* right, letting all those lovely details of life in ancient Egypt steer your voice into a style and register that are distinctly non-modern. The straightforward sentences with their tactile, sensory richness, presence of the deities, and deference to the complexities of rank, are deeply evocative of the ancient Egyptians' love of nature, their cultural diversity (woah, you did a *lot* of research!), and the constant sense of being surrounded by divine beings, magic, and earthly intrigues.
The way the you tell the tale, both with your descriptions of the settings and Harefre's voice, emphasizes the beauty, dangers, and above all *difference* of this far-off world. Your choice of first person is brilliant - it put me in the era and the story so immediately! But all the characters speak vividly - Severus, the querulous Khenti, benevolent (and rather Albus-like) Theshen, and Anum with his Fudge-like combination of ineffectuality and intrigues.
There were other overtones of canon for me - I don't know if you intended them, but I found them delightful. Like the way that even though the Pharoah's palace offers them comfort and relative safety, just like Hogwarts, Harry and Severus are still marked as outsiders by the differences in their lives. And the powerful vision of Isis, which for me resonated with the same feel of otherworldly power, joy and comfort that Harry got in Deathly Hallows when he turned the Ring and was visited by his parents. Isis's kiss had a very tender, Lily-like feel.
This fic enchanted me from the start with its well-pitched voice, fun characters, and rich setting. It ended far too soon, but with such sweet lingering images of Harefre and Severus journeying onward together. Perhaps to Heliopolis or over the desert to Punt, or across the Great Green Sea? Your Severus seemed so likely to be one of the Sea Peoples; from Crete, perhaps; he seems very like one of the slender, black-haired dignitaries in their famous wall-paintings.
LOL, can you tell you hit this old archaeologist's Egypt kink?
Tua atu! Which is to say, a salute of adoration to you!