There's most assuredly 3 girls and 1 boy here: Hibiki, Astolfo, and Satsuki, plus Max. That's three girls plus one boy!
This is an otoko no ko.
It denotes someone who, despite being a boy, has an appearance and personality that is undeniably that of a girl.Even girls, as long as they use boku to refer to themselves and have a boyish appearance, can sometimes be treated as an otoko no ko in fanworks.Oh!Ah... But I refer to myself with boku, but I have a feeling that I'm not treated like that.Eh?
To not be treated like an otoko no ko... That's prejudice!! Unfair! I'm jealous!!
