Kosuke Mizutani

Mizutani is quiet, emotionally burdened, and deeply affected by his relationship with Nanako. His grief dominates his behavior once the investigation begins reconstructing the incident from two years earlier.

He becomes fixated on responsibility for what happened, viewing the people connected to the incident through the lens of his loss.

His emotional state makes him difficult for investigators to assess because genuine grief and suspicious behavior exist side by side.

Mizutani has no supernatural powers or extraordinary combat abilities established in the film.

He is capable of independently researching the people connected to Nanako's past and following their movements, giving him enough information to become deeply entangled in the serial murder investigation.

Mizutani's relationship with Nanako becomes one of Conan's most important leads once the police discover that the murder victims share a connection to an earlier hotel fire.

Mizutani believes the people present during the fire abandoned Nanako and begins pursuing them in revenge. He plans to kill the people he considers responsible and then take his own life.

The investigation ultimately reveals that Mizutani did not commit the sequence of murders attributed to him. Kazuki Honjo and Conan uncover further evidence concerning the victims' actions and the actual killer, preventing Mizutani from carrying out his intended final act.

Nanako Honjo is Mizutani's girlfriend. Her death in the hotel fire leaves Mizutani consumed by grief and a desire for revenge.

Kazuki Honjo is Nanako's older brother and therefore connected to Mizutani through their shared concern for Nanako.

Conan Edogawa investigates Mizutani's connection to the serial killings and ultimately prevents him from following through on his planned revenge and suicide.