Wasn't Northstar just overly protective of his sister? She had multiple personalities and while one was fairly aggressive the other one was really meek & timid. As we found out he wasn't interested in women sexually and his sister is a female.
I just re-read my Byrne ALPHA FLIGHT run about 6 years ago, and I can't recall anything overt. Maybe Byrne just mentioned it as something he wanted to explore in an interview, and then never explored.
I remember the over-protectiveness.
I remember the split personalities.
And the gayness.
But I can't recall any confirmed incest.
So I withdraw that one, and give you Miracleman having sex with Miraclewoman in MIRACLEMAN 16.
And the gratuitous vagina-shots left-and-right childbirth issue (MIRACLEMAN 9).
Both those made me pretty uncomfortable.
