"Who are you?"
I don't understand why "who are you" must refer to a male. If I ask a woman who she is, how would I do that?
So, is this vocative case? I can't find it on your chart, and vocative is not included.
Why είσαι as opposed to είσαστε? If asking "Who are you?" isn't it rather likely to expect the formal over the informal?
"Eίστε" was one of the accepted translations, "είσαστε" has been added now as well!