Canon Touhou ftw. I can just feel Zun's yurifag spirit lurking in the murky subtext depths behind the presentation of Akyu and Kosuzu. It's not interesting enough to catch on with the mainstream of the doujin scene/secondary market, but it's moe enough for me.
I prefer the Kosuzu and Mamizou bits. They're a little more obvious. Akyu just seems to be a friend to Kosuzu.
Plus, if she keeps reading those Youma Books, Kosuzu may become a youkai herself, driving her away from Akyu regardless of her intentions. I'm kinda hoping that will happen.