After Satoko has calmed down, Chie puts her in the school infirmary. Keiichi asks his teacher how Satoko is and she replies that Satoko has fallen asleep. Chie tells him that she will take Satoko to the Irie Clinic soon. Mion tells Keiichi they should leave, and as he walks outside the school Keiichi is sure that left alone Satoko will only worsen, as anything the adults attempt will ultimately fail. Clenching his hand into a fist, he decides that killing Teppei is the only way.
Keiichi meditates on how he will conduct the murder, and asks his mother how murder mystery-esque books would describe the “true perfect crime”. She replies that a perfect crime would defeat the people of the genre, but innocently joins Keiichi in his thoughts. His mother asks him what the fundamentals of a story are, to which he answers “introduction, development, twist and conclusion...those things?” Still cooking, she nods and points out that without the crucial introduction there story never begins. “Nothing happens, so there’s no case. Since the detective isn’t called, there’s no investigation. If there’s no investigation, there’s no solution. In other words, this is the ultimate perfect crime.” Keiichi has a revelation, and quickly leaves before his mother says that “making it look like nothing’s happened...that’d be difficult in and of itself, wouldn’t it?”
Already on his bike outside the Maebara residence, Keiichi rides to the school and hides Satoshi’s untouched baseball bat (the same one he practices swinging with in ’’Onikakushi-hen’’) behind the school inside the side of a shed where a missing board conceals the weapon. He pedals a ways into the forest, and dismounting walks over to a small clearing. Picking up a stick, Keiichi hollows out a hole in the earth and realizes the area’s soil is soft enough to fit his plans. He smiles confidently, and returns home.
That night Keiichi phones Mion and sincerely asks her to take Satoko to the Watanagashi Festival, even if it is only for a small while. He says that if “she can be separated from that mean uncle...Satoko should be happy too, right?” She replies by asking him why he will not take her himself, and after pausing to let Keiichi stir up a meek excuse, she tells him that she received a phone call similar to his in the past—from Satoshi. “‘I’ve got something to do, so please take Satoko to the festival in my place,’ he said...” Keiichi has a flashback of when Irie informed him that Tamae Hōjō, the aunt, was beaten to death by a drug addict; he knows now that it was no druggie but indeed Satoshi Hōjō who murdered his aunt. Mion changes the tense subject and says they had already invited Satoko to meet up with the rest of the club anyway. Before she hangs up, she requests he tell her what he has to do tomorrow, “or are you not going to say, again like Satoshi?” He waves her away, tells her he is counting on her, and they hang up.
The next day while the festival is carrying on, Keiichi packs a shovel from his home into his backpack, and bikes to the clearing. He spends hours digging a ditch there, and begins to dwell back on his pre-Hinamizawa life. It is revealed that Keiichi at one time took the Krapelin test—Emil Kraeplin was a pioneer of research for manic depression and dementia praecox, or “premature dementia” (fitting for the Higurashi no Naku Koro ni series)—and performed exceedingly well in the intelligence portions of the exam. Keiichi’s mother wonders why he poor grades in school, which the psychologist explains:
“From the results of the Kraepelin test...we learned some very interesting things. Maebara-kun is poor at meaningless questions, and is unable to get interested in them. For example, if you tell him to draw a developmental view of a regular hexahedron, he doesn’t understand. But if instead, you ask, ‘if you open up a die, what kind of shape do you get?’ He can answer splendidly.”
The flashbacks continue, and it appears at one point in time Keiichi was enrolled in an advanced class in which is shown receiving full marks on a paper. Another scene reveals on the scores for his midterm exams in his first trimester of his first year, he placed third with a score of 671 (possibly out of a maximum 700, as the top score was a 698). The next event looks as if Keiichi’s good performances caused others to leave a dead rodent on his desk. As he continues digging, the past carries on with an image of Keiichi’s mother entering into his room to find him desolately spaced out on his bed; then it shows Keiichi riding a monorail (presumably with his mother, though it doesn’t show her) and afterwards entering the Hinamizawa school with his mother. His first shy encounter with Rena, Mion, Rika, and Satoko is made known, with the four of them smiling at him. They are next playing cards in their club activities, and it moves back into the plot with a recalling of Satoko stopping him from burning his house down and cooking dinner at his house. It is afternoon, the sky is orange, and Keiichi sits down exhausted from digging a fair-sized hole. He ends the scene with these words:
“It won't be long, now. Everything will be over. Everything... When the cicadas starts crying, tonight... It's over!”
Keiichi returns to the school and grabs the bat as storm clouds begin to roll over the sky above. He picks up a phone inside the staff room, and calls Teppei Hōjō’s house. He poses to be the Okinomiya Police Force, and tells the uncle that the police have Satoko in custody. Just before Keiichi puts up the phone, Teppei asks him where the police station is. Keiichi freezes, but the uncle recalls that it was next to the fire station. A determined Keiichi lies in wait nearby the spot where he dug the hole, and sure enough Teppei eventually comes quickly along on his moped/scooter with a cigarette in his mouth. Keiichi tenses, his eyes shine, and he squeezes the bat as the now grey sky thunders with storm clouds.
As Teppei drives through the bend Keiichi’s hidden in, the baseball bat-armed boy charges out and strikes the man down, his helmet tumbling off his head onto the ground as the moped falls over. A now demonic Keiichi stands behind him, and misses his next swing as the bat clunks against the soil. An inevitable chase ensues, and after running for a few moments the uncle glances back to see Keiichi nowhere in sight. He sneers to himself, but falls down the side of a hill to find the boy in front of him with wild eyes (though not the same eyes Rena and Mion had in Onikakushi-hen). Keiichi grunts madly, and rapidly swings at Satoko’s uncle over and over and over as blood splatters against him with the thunder booming overhead.
The rain starts to fall down, the festival is shown with people running to and fro trying to find shelter so as not to be soaked. However, completely unconcerned by nature, Keiichi pants in victory with a weary smile, and walks towards the bend where he struck out the first time to realize how far he would have to carry the man. Slowly wheeling the moped to the Onigafuchi Marsh, he pushes it into the murky waters. He says he probably misunderstood Satoshi, and tosses his baseball bat in as well. Moving faster, he realizes the hole he had dug all day was no more because of the rain and mud filling it back up. He takes his bike and speeds to his home, snatches the shovel, returns to the battered and bloody corpse of Teppei. Keiichi starts to dig a new hole when he hears a car horn blare from the road, but it passes by to his joy. After he covers the body and hole back up, he hides it with leaves and branches. Keiichi exults in his victory, laughing joyously as it continues to rain and thunder.
As he walks his bike back towards his house along the road (the shovel prevents him from riding) Keiichi collapses as a car stops a few feet ahead of him. When Keiichi stands up, he is puzzled by Takano stepping out of the car. She observes Keiichi’s shovel, lack of an umbrella, mud-stained clothes, and wet hair, to which Keiichi lies about going to the dam site with Rena treasure hunting. He claims to have forgotten the shovel and so had to run back and fetch it, as according to his excuse he didn’t think it would rain at the time. Takano replies, “even though this is completely the opposite place and direction from the dam?” Keiichi doesn’t reply, but tries to stand only to feel pain from his leg. Takano thinks he may have twisted it, and says she will take him to his house because she is a “good person” (foreshadowing). They have a small dispute over not being able to fit his bike in the already full trunk or the back seat, and ultimately Keiichi complies and leaves it in some bushes.
Inside Takano’s car, Keiichi looks into the back seat to find another bike, portentously similar to Tomitake’s bike Keiichi saw when he helped direct him to the Furude Shrine. A swift bolt of thunder prevents him from hearing Takano fully, only understanding “—ried properly?” When he asks her to repeat what she said, she replies with a minute grin (which causes Keiichi to fall into a state of bewilderment, shock, and fear): “Was the corpse...buried properly?”