This came in a subscription box, which is the only reason I was going to read this prequel to a series I was unfamiliar with.

I do think it is probably possible to read this as a standalone, but about 15% in there was a flurry of new groups and names and I just lost my motivation. 

I also think that reading the original series would help to understand why the mortals feel very Western Europe but the immortals loving in the same area were more Japanese inspired. It was a bit of a dinsonnnect for me that I would have only overcome for good characterisation. But while I liked the narrator, the others were a little flat. There is literally a bloodbath amongst the main group and I felt nothing about it, so it's a DNF for me, but I'm sure it would be great for those who love this world.