Mikaya, moving into an apartment investigates into the mysterious death of a man named "K" who used to live in the same room as the one he's moving into. The day he moves in, all the residents were doing a funeral procession in honor of K, but there was no body in the casket. Despite not having a corpse, everyone of the apartment is absolutely certain that K is dead. As the story unfolds, Mikaya dwells deeper into the mystery, and finds himself plagued by disturbing dreams of K. Mikaya's eerie journey continues in the manga's second volume, revealing his true connection with K and K's story.
- The talented writer in room 301 who all the tenants describe as handsome. People say that K looked young but seemed old. K hung around with the "deceitful girl" a lot, and even gave her one part of his puzzle ring. He gave another part of the ring to the gardener (G), across the street. K was also friendly with the Doll-maker and confided many of his problems to her.
- The new kid who moves into K's room. Mikaya asks all of the residents about K only to receive ambiguous half-answers.
- The Deceitful Girl
- A beautiful young woman who considered herself K's lover. She has an obsession with the idea of corpses rotting. After seeing Mikaya with a piece of the puzzle ring, she offers to trade the key to room 302 for it.
- A strange man who wears goggles all the time and likes to take baths. Together with the Morkwall collector, he finds K's body above the elevator.
- The Morkwall Collector
- A very nonchalant character who goes around the building everyday collecting "morkwall". No one, not even the tenants themselves, know what "morkwall" is but give it to him whenever he comes around.
- The Dollmaker
- A dark haired woman who makes dolls and rarely leaves her room. She has a faceless doll of K in her room that Mikaya is convinced is the body of K. It is the dollmaker who first guesses the identity of K's killer.
- The Butcher
- A well dressed man who goes around the building asking people for orders on meat and offers them a free duck egg with their purchase.
- An old engineer who serves as the utility guy for the building. He dresses up as a Priest for K's funeral. ;
- A nameless gardener who lives across the street from K's apartment building and always thinks herself too ugly for K's attention. G loves K's poetry and owns all of his published work.
It is speculated that K no Souretsu was inspired by Franz Kafka's novel, The Trial. The Trial's main character is named K. as well, and Mikaya's situation at the beginning of volume one is oddly similar to the dilemma in The Trial—Josef K. is arrested and put on trial for unknown reasons. Like death of K and his missing corpse, there is no description of Josef K's crime but everyone is sure that he needs to stand trial.