Demons are just evolved vampires, Miyabi could have just smelled Akira's blood.
Also, how tf did my man survive getting thrown THROUGH 2 massive stone pillars while already being half dead and then continuing to somehow sprint through the rest of the pagoda?
I'd rate this manga a 6/10 overall.
My thoughts on the series itself and the ending (and how It'd be more satisfying.) :
To sum it up (with no spoilers) : lots of loose ends, easy solutions and nothing really interesting done with the setting. A little more thorough exploration of class war...
Crazy to think that there's a sequel to this with like 168 chapters and then another ongoing sequel to that with like 200+ chapters...
Im going to guess the vaccine doesn't work on Miyabi anymore , or Akira fucks up the injection somehow.