Great work. I’m interested in where you will take this story. Keep it up!

Me still likey
Will Dessy have his arm cut off and be like Malik but less serious and edgy?
We shall find out in the next chapter!

I saw this fic on AO3, and given that most authors there don't like any form of criticism, I was pleased to see it posted here so I can tell you what I really think.

First, Desmond being paired with his ancestors became popular with esama's fics, and having read most of them (and noticing that her historical knowledge was profoundly lacking and didn't think Desmond bringing a sniper rifle would change history) there's something authors always forget: while there may be enough genetic distance between Desmond and his ancestors - Altair and Ezio being the most popular - he is, in effect, erasing his own existence or a different iteration of Desmond by preventing Ezio by breeding. While Ezio had plenty of illegitimate children (which led to the creation of Subject 16), if you change the past, you take away the futures of those who have not been born yet.

In your fic, you start the first half of the fic copying the end of AC III. I've played the game, I know what happens, and I don't need to re-read it. It's a sign of laziness. Add something new if you feel it cannot be avoided; otherwise, you are plagiarizing the game's writing.

Desmond is sent back in time to the Borgia attack on Monteriggioni, and I suspect he'll meet up with Ezio and have some great shenanigans before they start having sex. This iteration of Desmond may be a completely separate one from a different timeline, or it's the same Desmond from the original timeline. Either way, him falling in love with Ezio prevents Ezio from ever having children of his own. This major plothole is often forgotten by authors, and those who acknowledge offer some form of explanation but they are seldom adequate.

IIRC, you've also written an AC/HP crossover fic, and that's gotten you hits here and on AO3. I don't much care for HP, but if I can gather anything from this story, is that it's lacking in many departments. Copying from the game happens to be the greatest flaw. The introductory chapter will always sell your fic, and frankly, it seems like you're selling me a knock-off version here.

Oh, poor Dessy! I hope his arm doesn't get lopped off! And I hope Ezio doesn't try to rape him in his sleep(ignore that last one)
I love this story now, it's my baby and I can't wait for future chapters! See ya then!