Er..... how can a pic be both futa and trap?
I haven't seen the anime/played the game, so, can someone who has elaborate?

Well... I know Hamaji is a male. Why he has breasts, I'm not sure. Perhaps Otoha has something to do with it. But, since he is technically a trap, I believe it applies.

Can someone please explain this? I'm at chapter 3 of the anime and there's no sign of a trap around...who's the one that's giving? And PLEASE explain me how did they get here!!!

Just continue watching the anime, the trap will reveal himself in due time. As for this image, to understand it you'll have to ask a person who has played the sequel to H20, Root After and Another.