I just wondering why so many people(player) call her Hokusai instead oui if they already know that she's Hokusai daughter?

Calling her Hokusai rolls off the tongue a bit better :P

Besides, you're not completely off, in her 3rd Ascension, they merge and in general, they're synonymous as a servant.

Oh yes you right I forget about 3rd ascension 😅

And does that mean she counted as gender bend servant or not?

I call her Hoku. I shortcut everything

Oui ~ hokusai was the squid right? 😅