Cock seedbed slimes

Due to the fertility of futas and the fact that 99.9% of STDs are eliminated from the genitals of females through futa dick. Futas created a natural enemy from STDs due to STDs needing to rely on other sexually transmitted diseases for survival. Over time, the non-cooperative viruses died out, while those specialising in the same format became almost extinct, leaving the only real/viable enemy to be the evolving colony cells of STDs.

Rapidly, due to adventurous and greasy skanks, the STDs evolved into slime-like creatures from isekai games and stories. These slimes quickly adapted thanks to the proper growing environment and because the STDs are the durable ones that have at least survived sperm and cock attacks. In a way, futas fostered and fathered these slimes since the slimes took up human forms based on individual sperm cells, something that came back to bite the voracious swimmers. Now, instead of getting obliterated by sperm cells, the slimes were turning the cocks and balls of futas into spawning grounds for more slime girls, giving futas unending pleasure as they continuously swell their sexual male organs. Even with extensive treatment, a futa is likely to be plagued by the slimes again, thanks to microscopic slime remnants, forcing futas to amputate their cocks and balls and turn to using their pussy cocks of cocks of foetuses, as well as a hyper-stimulated clitoris.