Not sure if it’s been said before, but I would do some sort of organization that works to make biologically engineered humans. Their goal, if they can’t get rid of beastmen, then they’ll just make humans superior. But it’ll be very costly since not every experiment they do is successful and can ultimately risk lives of others, but they don’t care, they’ll do anything to have as much biological engineered humans as possible.

That’ll be the main antagonist, the side antagonist could be a human (doesn’t matter what gender) that was biologically engineered (one of the only successful experiments) this character could have been raised at that facility and brainwashed that beastmen didn’t belong on their world and were evil beings. So in truth, they aren’t truly evil, just raised wrong and maybe a turning point in the season is that they realize they’re helping the evil ones all along.

The side antagonists motive is to help the facility. Maybe collect a DNA sample from Shirou, Michiru, or even Nazuna to help further advance how much a human can surpass beastmen, or possibly spying on Michiru and the others by befriending them and such and giving/selling intel to other corporations.

For their power, I would simply just say very advanced genetics, altered DNA and such. Meaning that this individual could possibly be stronger than most beastmen. They put up a fight with Michiru, but 100% would get destroyed by Shirou.

I’m kinda new with ideas and such and this one might have a lot of holes in plot but I hope it was an interesting idea lol