Ryôji Morimoto

Ten thousand years ago, a massive battle known as the Battle Royal was fought by fifty-two Undead, each representing a species fighting for dominance over all others. The winner was the Human Undead, known as Category Two of Hearts, giving dominion of the Earth to humanity. In the present day, archaeologists discover the sealed Undead, and accidentally set them free. Thus, a new Battle Royal begins. (mydramalist.com)

Ryoutaro and the DenLiner gang have set up a detective agency called the DenLiner Police who seek to catch the Imagin who stole a spare Den-O pass from the Owner and find the Imagin who has built a crime syndicate with human criminals.