To those unfamiliar with Magne's Quirk, Magnetism, it gives those it affects a polarity based on their gender, which is North for women and South for men. Since RH Junior doesn't have a good opinion of transgender individuals, it follows that he'd insist that only Magne's biological gender matters and insist that she, being biologically male, be designated as having a South polarity as far as her power is concerned.
And yes, I know that Magne's Quirk canonically doesn't work on herself, but RH Junior plays fast and loose with other Quirks, so maybe he'll have her get her own polarity to prove his point.
His being transgender is only revealed in his character profile, so it's easy enough to ignore that aspect of him in the fic, and him being a hero means he's less likely to end up being bashed for being trans.
