Stone's Cocoon(2015)

Stone's Cocoon is a Japanese crime thriller series centered on a gruesome murder investigation. When a body is discovered encased in concrete in an abandoned building, a mysterious criminal calling himself Tremi contacts the police to taunt investigators and offer cryptic clues about the killing. Detective Kisaragi Toko, newly transferred to the First Investigative Division, becomes the department's negotiator. As Tremi's psychological games escalate, a second victim surfaces with their head sealed in concrete, confirming the killer's twisted pattern. The investigation deepens as Toko and her team attempt to uncover Tremi's true motive and obsession with concrete entombment. With each cryptic message and calculated murder, the criminal's real target gradually emerges, pushing the negotiator into a dangerous cat-and-mouse game where understanding the killer's psychology becomes essential to stopping them.