@secretagentfan thanks for showing up! that was really interesting!
i want to reply to all of it later, but i'm a bit busy at the moment, so let me just propose this for now:
we don't know much about how the veela are viewed by the wizarding world in canon. given their general attitude towards other magical creatures, it's not too much of a stretch to imagine that they don't treat them very well, right? and if nezumi is actually half veela (instead of just 1/4 like fleur) then it's very possible he's gotten sh*t his whole life because of it. since there's not much about veela in canon (and this is an AU) we could easily make some really sad headcanon like half the veela got wiped out by wizards or whatever. because you're right, the nezumi-is-mad-at-where-shion-comes-from thing is important.
...what if he doesn't even go to hogwarts. what if he taught himself magic and lives in the shrieking shack, and then his life is really interrupted when werewolf!inukashi shows up in there one day.
too much of a stretch???