Saku is getting so good but chapter 22 (and 20 and 21) definitely threw me for a loop when trying to figure out how to place this series in the Vampire Miyu universe.
I thought it followed after volume 10 of the manga because Ranka is the guardian of the 2nd tier (as opposed to her role in episode 2 of the OVA).
But then there’s the alternate versions of Carlua and Pazusu (different roles than in New Vampire Miyu) and in 22, Miyu makes a callback to Lemures as if she’s already dealt with him (I.e.; returned to the darkness).
Maybe they retconned New Vampire Miyu and possibly chapters 2-3 of the original volume 3 (Deja Vu) and chapter 1 in volume 8.
Or Saku picks up after the original volume 1 (Origins).
Wouldn’t mind hearing from others if there are other possibilities.
Well, in the original Japanese version of the actual Manga itself, Miyu just calls Black Kite/Tonbi a "Dirty old man" and doesn't mention Lemures at all. But I am as confused as to where this manga stands with the original manga series as you are and am hoping to find some answers. I think Narummi Kakinouchi and Toshihiro Hirano are the only ones who know since they are the people who made this.
As well as that, I heard mixed results from my various searches for answers as to where Saku stands in the manga's timeline. Some say that it takes place at the early points in the series, (which would be weird considering that Saku has characters that use smart phones and social media), while others say it takes place in a separate timeline entirely.