Six years ago, the right half of a corpse was discovered. The left half was never found…until six years later, completely fresh with no signs of decay.

Now, Special Agents Mizuki and Ryuki, along with their AI partners Aiba and Tama, are tasked to solve the bizarre Half Body serial killings while unveiling the mysterious plot known only as the Nirvana Initiative…

[From Official Press Release]

Six years ago:
The right half of a body suddenly appeared at the studio for an online quiz show. Rookie investigator Ryuki is assigned to this strange murder case.

Present day:
The left half of the victim's body is found many years later, and the case is opened once again. New recruit Mizuki makes contact with the case's former investigator, Ryuki.

[From Weekly Famitsu 4/28 story description]