Once again, fate is consumed by insanity...
Every year on the same day, one person dies and one person disappears...Such "coincidences" continue to occur in the remote village of Hinamizawa. Keiichi is accompanied by Shion, the twin sister of his good friend Mion Sonozaki, and violates the village's rules. And this year's "curse" begins again.
Watadamashi-hen Part 1
June 12th, 1983. Keiichi and the club members play in a games tournament in Okinomiya. Keiichi struggles to find a lead in his group’s game as Rena, Satoko, and Rika effortlessly win their games. Mion comments on Keiichi’s apparent failure to take the game seriously. Keiichi gets serious and manages to win the game, but Mion says she needs to go to her part-time job and postpones the tournament. They’ll be continuing things at the Watanagashi Festival. The group decides to split so Rika can practice for the ritual dance and the shop owner comes out with gifts for everyone. Everyone except Mion receives a present, with Keiichi receiving a doll. He considers giving it to Mion but she might not like it, however Mion eyes the doll from the side. Rika pokes Keiichi and tells him that no matter who he gives it to, they can’t reject his feelings. Keiichi decides to give Mion the doll. She reluctantly takes it but seems to be very pleased with it.
Everyone goes home, and Keiichi stops at Angel Mort for lunch. Keiichi gets caught off guard by the risque outfits worn by the waitresses and runs into Mion, who apparently works there too. After an awkward pause, Keiichi realizes that he can use this chance to get revenge on Mion for prior punishments. Keiichi teases Mion a lot and makes her blush, saying that he never expected this side of her. Mion explains that she is actually Shion Sonozaki, Mion’s younger twin sister. Keiichi apologizes for teasing Shion and says that the uniform would never look good on Mion. Shion asks what he means by that when she’s called off by another waitress. Keiichi leaves, believing that Mion was just pretending to be a twin.
The next day, Keiichi goes home from school hungry, having skipped lunch. Shion follows him home and brings him a bento set, as thanks for the doll. Keiichi is confused since he gave Mion the doll, and Shion gets flustered while saying they share the same tastes as twins. Shion was happy to reward Keiichi on Mion’s behalf and soon leaves. Keiichi devours the bento.
The next day, Keiichi walks home with Rena and accidentally mentions Shion. Rena asks who that is and Keiichi explains that she’s Mion’s twin. Unlike Mion, Shion seems like a cute girl. Rena says Mion’s been in a good mood as of late and compliments her for her femininity. Rena says that though Mion is their club president, she too has a cutesy side. She hopes that out of all people, Keiichi will keep that in mind. Keiichi thinks that he would really like to get to know Mion and Shion better.
Keiichi heads to Angel Mort and gets lost in his daydreams, knocking over some bikes. A bunch of delinquents appear and start berating Keiichi when Shion appears and demands they let him go. When the punks show defiance, many villagers nearby drop what they’re doing and join Shion, intimidating the boys with their menacing presence.
Watadamashi-hen Part 2
At Angel Mort, Keiichi thanks Shion for saving him back there. He wonders what was up with the villagers acting so weird, and Shion explains that for the longest time, Hinamizawa’s villagers have had a sense of unity. Anyone’s enemy becomes everyone’s enemy. Those bonds of unity stemmed from the dam project started ten years ago, which was cancelled thanks to their combined efforts. Shion leaves to go to work and Keiichi says he owes her one, still calling her Mion.
Keiichi goes to the Furude Shrine to assist with festival preparations. Shion gives Keiichi some barley tea to help him cool off, and as he drinks it Mion appears holding two cups herself and screams in annoyance. Keiichi nervously looks between the two girls, realizing that Mion and Shion are truly separate people. Keiichi asks if back then, it was Mion who claimed to be Shion the first time he went to Angel Mort, and if it was also Mion who brought him the bento and saved him from those delinquents. Mion gets flustered as Shion giggles.
Tomitake and Miyo Takano arrive, along with Ooishi. Ooishi hopes things won’t get too complicated for this year’s Watanagashi, and Keiichi asks what he means when Mion suddenly asks him to go for a snack. They start to leave when Takano wonders aloud who will die and disappear this year, distracting Keiichi. Mion tells him to ignore her but Keiichi stays behind. Takano tells Keiichi about the yearly deaths and disappearances that have occurred ever since the dam war ended and speculates that there has to be a human force behind them. Keiichi yells that can't be true but then remembers the menacing air the villagers had when Shion gathered them earlier. Takano leaves Keiichi wondering if the villagers could really be planning the curse.
The festival begins. Keiichi watches Rika’s ritual dance when Shion appears and motions for him to come with her. They meet Tomitake and Takano in front of the ritual warehouse in the woods, where Takano plans to break inside and see what lies within. Keiichi and Shion follow as Tomitake stands guard. Inside the warehouse is a statue of Oyashiro-sama and many strange tools. Takano educates them about Hinamizawa’s past, their demon ancestors, and the purpose of the original Watanagashi.
Keiichi gets creeped out and bumps into the Oyashiro-sama statue, causing its head to fall off. Tomitake enters the hall upon hearing the noise. They fix the head, which seems to have split in half before it fell. Keiichi puts it back atop the statue and sees a slot in the neck area, wondering if that was there to begin with.
The group leaves, and Shion tells Keiichi that if the curse passes then those four might be the victims because they trespassed in the storehouse. After Shion leaves, Keiichi ponders this as a pair of arms grab onto him from behind.
Watadamashi-hen Part 3
Rika happily says she’s found Keiichi after grabbing onto him. The other club members follow. Mion asks Keiichi if he met Shion at all today, and he denies it. She also asks if he saw Tomitake or Takano, and Keiichi denies that too, thinking he can’t let Mion know they trespassed. Mion grabs Keiichi and says they need to do the cotton drifting, makig Keiichi think of Takano's gruesome story.
At the river, Ooishi suddenly appears. Mion tries to ignore him but Oosihi tells Keiichi that Mion is part of the Sonozaki family, a yakuza group, and she can have people killed without leaving a trace. Keiichi defends Mion and says she would never do things like that. Ooishi asks if Keiichi met Shion, Tomitake, or Takano that night. Keiichi denies it, wondering why Ooishi asked the same thing as Mion, and the detective replies he *knows* Keiichi met them earlier and walks off. Keiichi is horrified that someone saw the trespassing and Mion says to just ingore everything he says. Mion gives a strange look in Ooishi's direction and says that she’ll always be on Keiichi’s side no matter what.
Keiichi goes home that night and gets a call from Shion, who asks if he saw Tomitake and Takano at all ever since they left the storehouse. Keiichi gets concerned since everyone was asking that question and asks why Shion wants to know. Shion says Tomitake and Takano have gone missing: Witnesses say they stole a vehicle from the festival parking lot and drove off in it. Shion believes they ran away because they knew they were in danger from the curse, and that she and Keiichi are next. Keiichi swears that he wasn’t interested in trespassing and never wanted to be involved. He blames Shion for dragging him into this and yells how she’s going to make up for it when Shion suddenly hangs up.
The next day at school, the teacher Chie tells the class that Mayor Kimiyoshi has been missing since yesterday and that all the students should leave school in groups when they go home. Keiichi is confused since the mayor should have nothing to do with the trespassing. Rika also seems concerned. At lunch, Rika excuses herself and says she’ll go home since her stomach hurts. Keiichi gets up and begins to go after her when Mion stops him, saying that Rika will be fine but is more worried about him. Keiichi thanks her for caring and goes after Rika.
Keiichi goes outside and calls out to Rika, saying they should walk home together when Rika starts cackling. Rika says that no matter what Keiichi did, this world is over. A strange glow appears in Rika’s eyes as she says that if Keiichi was a good boy and just watched her dance, then nothing would’ve happened. Keiichi is scared by her sudden change. Rika is very sure that Tomitake and Takano are already dead despite their corpses not being found, which may or may not be good for Keiichi. Rika goes back to normal and thanks Keiichi for looking out for her before walking off by herself. Keiichi wonders just what has been going on ever since the watanagashi.
Keiichi goes home and gets a call from a worried Satoko, who says that Rika never came home. She asks if Keiichi talked to Rika earlier, and Keiichi regrets that he didn't follow her. Keiichi joins Rena and Mion at Rika’s shack and asks where Satoko is. Rena explains that the front door was locked, and they haven’t gotten any responses no matter how long they call. Keiichi regrets getting the girls wrapped in the curse and yells inside the house, but gets no response. Rena goes to the assembly hall to get the keys. Keiichi gets a ladder and climbs up to the second story window as Mion holds it in place. Mion says that nobody would ever put Rika in danger since she’s head of the Furude family, and when Keiichi asks what she means, a strange look appears in Mion's eyes as she says she has to end it.
Mion rambles that Rika is behind Oyashiro-sama’s curse and is going to kill someone using the Three Families, shaking the ladder and startling Keiichi. Mion swears she’s going to put an end to the curse, her ladder rumbling growing in intensity until Rena returns with the keys. Mion goes back to normal, and they soon find that nobody's inside. Mion says this will all end when the higurashi cry and asks Keiichi to come to her house, wanting to tell him something.
Watadamashi-hen Part 4
Keiichi follows Mion to the Sonozaki main house, aware that she must know what’s really going on. Mion puts on a kimono and tells Keiichi that Rika is gone. Rika is supposed to have very close ties with Oyashiro-sama, and that as the current head of the Furude family she has been chosen to be a sacrifice. Keiichi apologizes for trespassing into the ritual warehouse and bows his head in remorse. Mion says many people have taken offense to it, but assures Keiichi that his sin wasn’t what doomed Rika. Mion accepts his repentance and repeats that she’ll always be on Keiichi’s side.
Mion takes Keiichi to the underground torture chamber. Though it looks similar to the inside of the warehouse, Mion explains that none of these tools have seen actual use. Keiichi continues to believe in Mion as she takes him to a safe room, which has food, electricity, and a toilet. Mion then pushes Keiichi into a jail cell and locks it, asking if he remembers the game tournament and the doll. She was very happy when Keiichi acknowledged her as a girl and expresses her love for him. She promises to protect Keiichi and not let anyone kill him, saying that if it comes down to it then Keiichi can play the part of the victim and act like Mion forced him in there. Keiichi asks what she plans to do.
Mion says she’s going to end Oyashiro-sama’s curse, explaining that the villagers’ sense of unity has become warped such that they antagonize anyone who opposes them. The Sonozaki family has always led the Three Families and enabled this tradition, and Mion believes it is her duty to end it. Keiichi says he wants to help when some rumbling noises are heard. Mion laughs, saying that someone’s minion decided to show up. She looks at the security system and pulls out a revolver, reminding Keiichi to pretend like he’s the victim.
Mion leaves and Keiichi starts ramming into the cell door, trying to get it open. When the door fails to open, he thinks about Mion and collapses crying. Keiichi is rescued by the police sometime after, with Ooishi saying they never would’ve found out about it without a nearby officer hearing a gunshot from the estate. Ooishi says they investigated the well inside the dungeon Keiichi was in and found the corpses of Oryou Sonozaki, Kiichirou Kimiyoshi, and Shion Sonozaki. At school, they found Rika’s corpse inside of the septic tank. Additionally, Satoko and Shion were found dead next to each other in the Sonozaki estate. Keiichi thinks about Mion supposedly saying that all these places were safe and wonders if Mion was really the one who killed them all.