Crimson

From Bliss :
In this universe, there are four worlds: Meikai, the center of the universe, Ninkai, the human world, Youkai, where monsters with shape-shifting forms live, and Shintenkai, the world of the Celestials. Shiba Yukinari is one of the few who are born of both Youkai and Celestial blood - during the day, he works as a detective, but also has the job of exterminating youkai. As he works collecting 'cores', or a youkai's source of power, he meets Riifei who that demands that Yukinari hand over his own 'core'...

Vol.1 Crimson
Vol.2 Crimson Crown
Vol.3 Crimson Chaos