To use an example: Abe Sapien was fucking Liz Sherman in the Hellboy comics and also the animated movie adaptations:
but in the 1st LIVE movie adaptations they instead ship Liz with Hellboy because his demonic invulnerability to fire (actually just high DR in general if you look at his GURPS stats) allows him to kiss her and shit while her pyrokinesis goes out of control with no danger to himself.
Now here's the thing: yes, Abe was pumping his cum into Liz's vagina, cumming on her chest, etc.
But she basically has the ability to "purify by fire" her entire body because she too is immune to fire, and can basically just sterilize herself of all bacteria / sperm the same way you would use fire to sterilize tools prior to surgery.
So it's a lot less disgusting if a foid could be fire-purified of cum. Not as good as true virginity mind you, but still better than imagining all the cum particles lurking on the bodies of your average roastie.
Now if you think of Nova + Human Torch, both of them are producing high-temperature flames, neither get damaged by it, and any ejaculate on Nova's body from Hulk or Silver Surfer or whoever else she fucked prior to Johnny is going to get vaporized.
That's assuring, somehow.
