Futanari is an interesting subject.
Basically it's what a girl would be like if she had a penis and testicles.
I found some Futa-Ballbusting stuff, figured I'd share it with you guys:
http://g.e-hentai.org/s/7ad83bac2b/528085-1
From the comic, the low blows they receive don't really take them down… which makes me wonder… would a Futanari's balls be less sensitive than an actual human male's?