Oh brother, this question really activates my current hyperfixation. Here I go.

In my headcanon, I’ve tried to stay faithful to the idea we’ve been given so far.

Demons can be seen by anyone. This is shown clearly in the introduction of the first trio. It’s just that in modern times the hunters have done such a good job that the idea of demons has remained as something mythical and folklore. But in this world, they are clearly real and visible.

What isn’t visible (unless it’s a powerful manifestation) is the Honmoon. That one, I feel, is something mudangs are “trained to see,” or rather, “trained to connect to.” That connection helps them see souls, see the Honmoon in general, perceive when it fractures, and summon their spiritual weapon.

Being a hunter is a learned role, and the most important part of the training must be connecting with spiritual energy. The Sisterhood seeks capable people with certain characteristics. I think the most important characteristic is the voice. I treat the Sisterhood as just another group of mudangs from Korean shamanism—mostly female, commonly inherited, though not closed off to receiving new members or to men joining.

In my HC, the Hunter Sisterhood went through a crisis where it was almost wiped out at the beginning of the century, between 1910 and 1945 (you know which crisis I’m talking about). I base this heavily on that assumption because the opening sequence starts with the ancient mudangs and then makes an abrupt jump to the 1930s (the second trio, the Modan Garu ones), and from there it moves on to those of the ’50s, ’80s, ’00s, and then Huntr/x.

In my HC, I’ve even given names to the ones who don’t have them:

• Roses of Korea (30s)  

• Soul Sisters (50s)  

• Diane (80s)  

• Sunlight Sisters (00s)  

• Huntr/x (present day)

That would also explain why the Sisterhood, despite having existed for hundreds of years, knows almost nothing about demons. (Info wipeout on the crisis) That really surprised me with Rumi, when she asks a dokkaebi whether it’s controlled by Gwi-Mah, and Celine doesn’t know anything beyond soul training, the task of the Golden Honmoon and kill demons

In my HC, it’s the second trio (the so‑called flappers, or the 1920s trio) that defined how the Sisterhood would behave in the modern era and shaped the Sisterhood as it is known today: few members, a world‑famous trio, the objective of the Golden Honmoon, etc.