This is a bit specific for a yandere Witch Hat Atelier idea but...
I was imagining a female Reader becoming the target of the Brimmed Caps after one of them witnesses you, an outsider to magic, having a rather lovely and inspiring conversation with a child where you encourage them to pursue magic "no matter what" and perhaps you even give the child a special little 'magic charm' of your own that, even through guesswork may be impressively close to being a spell for... something, proudly declaring that you "like to make your own magic" and something about how "there are so many beautiful and unexplainable things in this world just waiting to be discovered, and magic is just one of them"
Perhaps you've even coincidentally had lovely conversations with certain other lovely blonde-haired children the dark magic users have had their eyes on, further showing both your love for learning of the craft and for further inspiring that same desire and hunger in others
So the Brimmed Caps, naturally, respond to this by. Selecting you and performing a ritual on you using Forbidden Magic where, all you can remember are hazy memories of chanting and candles and caresses, symbols drawn on your body, on your belly, symbols that remain as you awake alone in your home with the realization that you are now undeniably pregnant; the morning sickness you begin having out of nowhere only confirms it.
You're stuck between being terrified of what could happen to you, and yet... you can't help but feel your heart swell at the idea of raising a child of your own.
Meanwhile, here's Qifrey, barely containing himself from openly showing just how crazy it's driving him to watch your belly slowly grow with life as you remain under his watchful protection, keeping an eye out for the Brimmed Caps' suspected return. Qifrey who gently coos about how nice it would be if you had a daughter and "gave Coco a little sister to play with and teach magic to", not only being genuine but also absolutely fantasizing about getting to plant his own seed in your belly and create a child with you all of his own
At the same time, you're under the looming threat of the Knights Moralis and Easthies who are lowkey arguing they should wait to let you give birth, take your child, and then wipe your memory, since there's no way of knowing what the child even is given its origins, or so is their fear, as you and Qifrey naturally argue that that is SO horrendously unethical it borders on torture
Meanwhile Iguin and his fellows, who have formed a cult-like adoration and fascination with you of their own, simply used magic to ensure you became pregnant and nothing more, with the child otherwise being completely normal and healthy. In the same way that they won't allow their talismans to be tampered with and traced back to them, they will not allow any meddling in your pregnancy. If anyone so much as tries to draw some sort of Circle of Abortion or otherwise, that room will be filled with as many skilled magic users as needed, if the sigils on your body aren't outright capable of yanking you to safety where you will then be tended to by a cult that is particularly infatuated with you
It's hard to say which team of your "protectors" you should fear most, but one thing is for certain: any sort of control or influence over the future of you and your child has been taken from your hands. You're all but helpless against those far more knowledgeable in accomplishing miracles than you ever even conceived, and if they want to use those gifts to watch you, track you, entrap you? You're completely at their mercy, whether those that want to do so consider themselves your friends, your allies, your protectors, or even your lovers.
Even as you continue to learn magic, as amazing and impossible as it is, you'll still be powerless against them.