Before the raid on Depths of Palm (Gold of the Kunie) in Susukino where Shiroe looks for full party members, Naotsugu and Regan find Tetra. Later on in the raid of Depths of Palm, Tetra joins (or is permitted to join) Log Horizon.
It seems that all members of Log Horizon, except Naotsugu, know that Tetra is actually male. How is that?