Obviously female kaijin: Probably male kaijin:
So something interesting came up in the episode 3 thread. Apparently, the official Portugese dub or sub actually makes the distinction of whether these characters are male or female. So Luckyuro and Bomper are definitely males. While Navi is an "it". This post
Plus Luna has consulted with actual Japanese people, who seem to agree that Izayoi is also male. After initially thinking that he was male, I have to agree with people that there's too much evidence in support of him being male. He doesn't look female (see comparison pics of obviously female kaijin to ones who aren't), he's a page, and there's a definitely Ranmaru vibe that several people have picked up on.