I get the feeling that haruki cross dressing friend is either gonna A) unlock a new fetish via cross dressing or B) get the ts virus.
Only thing we know of the gender bending process is that the mom said that Haruki already acted girly and was in love with the big brother even when he was a boy.
Haruki could possibly have wished to be a girl, and this may be the trigger for whatever magical effect that causes the gender bend.
Who knows, maybe this boy being gaslighted into liking being a girl may legit end up triggering the gender bending spell.