Atisse is a guy.
It is implied that might've taken the form of someone he really cares about like ephry, hence why he looks like a woman
Is it implied? He himself said he's a male. I mean, Han-bin saw him naked, too. He's a different kind of dragon to Ephyr, not just appearance-wise but also because he can switch forms unlike Ephyr. Ephyr permanently changed herself with that medallion, but Atisse obviously didn't use it to take on someone else's appearance since he can switch between his dragon form and human form.
I'm just stating what I've read. I'm not saying you're wrong.
No worries dude, I don't really know it's just the way I interpret what/how he said it or his explanation ¯_(ツ)_/¯
I haven't finish reading it but is Artis a girl or a boy men I am confused