A man-eating yokai who killed Reimu. Real name: Sou Otogiri (Alias). Species: Yokai. Gender: Male. True name: Unknown. Age: Unknown (approx. several hundred years old). The protagonist of this story. He has short white hair. As a man-eating yokai, he survives by periodically eating villagers. He is currently staying with his benefactor, Ryo (whom he calls Ryo-san). He is accustomed to killing and can cast powerful barriers, such as those that absorb sound or make a specific target invisible to everyone but himself. While he is fundamentally kind-hearted, he is ruthless when it comes to killing, though he occasionally wonders if his actions are right. He harbors a wish that if he had been born a normal human instead of a man-eating yokai, he would have liked to live a life of laughter and mutual aid with others. He maintains a friendly relationship with Marisa. "I just don't want to die..." He killed Reimu because she discovered his feeding habits, and he acted out of a desperate need to survive.

Full name: Reimu Hakurei. Gender: Female. Species: Human. Age: Unknown. She has long brown hair reaching down to her waist. Reimu realized that Sou was periodically killing and eating villagers and attempted to exterminate him, but was killed by Sou instead. Her body was not eaten by Sou, but Marisa later discovered her purification rod lying in the grass within the forest.

Full name: Marisa Kirisame. Gender: Female. Species: Human. Age: Unknown. She has blonde hair that falls between her shoulders and waist. She was Reimu's best friend and is deeply enraged by her death. If she discovers that Sou is a man-eating yokai and the one who killed Reimu, she intends to kill him. She learns that Sou is the culprit later in the story.

Full name: Remilia Scarlet. Gender: Female. Species: Vampire. Age: Approx. 500 years old. She has short, shoulder-length purple hair. As the mistress of the Scarlet Devil Mansion, she possesses the ability to manipulate fate. Although she didn't know who the killer was, she knew Reimu was destined to be killed. While she can change minor obsessions with her power, the weight of this particular destiny was too great for her to alter. She has never met Sou. When Marisa eventually realizes Sou killed Reimu and tries to fight him, Remilia intends to intervene. While Marisa buys time, Remilia plans to throw her Spear 'Spear the Gungnir' from behind, imbuing it with a powerful destiny of death to pierce him. She does not initially know that Sou killed Reimu.

Full name: Patchouli Knowledge. Gender: Female. Species: Witch. Age: Approx. 100 years old. She has purple hair reaching down to her waist. Born with a weak constitution, she rarely leaves the library of the Scarlet Devil Mansion. However, after Marisa returned the library books she had claimed she would keep until death, Marisa asked for her help in finding evidence of Reimu's killer. By tracing the residual spiritual energy left on Reimu's purification rod, Patchouli managed to narrow down the culprit's approximate location. She has never met Sou.

Full name: Ran Yakumo. Gender: Female. Species: Youkai Beast. Age: Unknown. She has short, shoulder-length blonde hair. She has nine tails and is the shikigami of Yukari Yakumo, standing as a top-tier youkai beast. She happened upon Sou while he was killing and eating a thief who had broken into Ryo's house, drawn there by the moonlight. Realizing he was Reimu's killer, she tried to kill him but was nearly killed herself; Sou stopped at the very last moment. Sou then placed her under a barrier in Ryo's house that makes her invisible to everyone but him, prevents her from interacting with anyone but him, and restricts her power to that of a human's level. She cannot leave the barrier, though she can move within Ryo's house and touch Sou. Ran has since given up on trying to kill Sou and has become somewhat kinder toward him. She learns the full details of Reimu's death later on.

Full name: Yukari Yakumo. Gender: Female. Species: Yokai. Age: Unknown. She has long purple hair reaching down to her waist. As a Sage of Gensokyo, she mourned Reimu's death. She eventually comes to believe that the man-eating yokai who killed Reimu is holding the missing Ran hostage. She learns that Sou is the one who killed Reimu later in the story.