I have another question why doesn't the other classmates know about that the main character is a male since they go through some sort of portal from earth to the magir realm or they have been born their
The game tells you the reason.
Pretty sure it was because those people already know he is male, and/or because they were with him when the illusion was cast. I'm leaning towards the first half.
However for the ones that he hadn't met outside of the casting of the spell, they see him as a girl because of the spell.
I might be mistaken slightly, since I haven't played this game in a while, but I do definitely remember that an illusion spell was cast.
- Edit: I just remembered a scene in the lady's office where she tells him that if anyone finds out he is a guy, the illusion will break- but only for that person. I'm keeping all of that cuz I'd rather not have typed all that out for no reason.