The top one is Crona's sex so it's what he biologically is. Gender is what YOU process as. Crona has never clarified for us so yes it is unknown. Either way Crona is still my favorite. Right above Kid.
I seriously thought that Crona was a girl when I first saw this, and when Soul and Maka kept on referring him as a "he", I thought that somebody was gonna pop put and be like, he's a GIRL. Until Crona said he had problems with ladies.