For those who don’t know, this series seems to have grown out of the author’s touhou fanfic, focused on the secret sealing club characters, and become it’s own thing.
TIL. So that's why I always felt some similarities.
The SSC is such an underrated piece of lore in Touhou. Definitely worth a reading!
(You can find the stories in the Touhou wiki, I recommend reading each paragraph while listening to the associated track to set the mood).