How many Black Knights (Black Wings Generals) are there really?

But yah like it's been said. Trailers present Aran as a female, so do some npc and that anniversary event, but meanwhile some other npcs and cutscenes imply that Aran's a he.

The official and true gender of Aran in game remained as a confusing secret like Crona 1

Anything that happens outside the game or during events means nothing, in no way during actual in game events has Aran been shown as female so canonically Aran is a male.