transcribed 2parter lore — seed

When they were being created, the scientists retooled the system of checks the body usually does to ensure sperm is formed properly so they can be performed faster and more efficiently. Similar changes were made to the egg cell creation process. Both processes were kept in line with existing heat/rut cycles so as to not interfere with the sanctity of any one species' biological processes that happened to be in line with them.

This did more than the hypervirility and hyperfertility experiments could, in short, though the full effects likely have not yet played out.

Their antiheat pills have the same effects as any others, reducing the desire to have sex and the biological indicators if not eliminating them entirely. It does not make them infertile.

Twoparters fire blanks during any time that isn't their cycles, as their bodies will largely not make sperm or eggs, or if they do, just as a check to ensure they still can before breaking them down for nutrients. (Though they can and often will still engage in sexual intercourse, largely because the circuitry that makes it feel good doesn't shut off, though the results are comparably lackluster alongside the alternative.)

This physically produces a different, stronger cycle sensation than most, litter sizes double or triple the average for their species, and volumes of ejaculate that not only are between two and ten orders of magnitude greater than their species' average (the assumed average typically being a few milliliters at a time), but also have a high sperm count. This makes the fluid itself look no different but behave as more viscous than molasses, requiring a high rate of ejaculation to be eliminated from their system. Those that get ejaculated in or on by one say it's like getting punched or slapped in those places, often adding to their erotic appeal.

Some like this attribute enough that they elect not to take the pills, though for reasons of population control those themselves are opt out, and the ace/aro/acearo among them definitely appreciate the pills not being opt-in.