I love you, Grandpa! I don't want to do this! I'm sorry. ~ Mion to Shion as she strangles her to death. As the next head of the Sonozaki Family, I must protect Keiichi. Satisfied at hearing Mion's confession, Satoko finishes her off before turning the gun on herself saying that she'd be seeing them in the next world. Mion laughs gloating that she had wrung Rika's neck and tossed her body into the septic tank saying that either she personally killed her, or she drowned in the excrements. Unfortunately for her (due to teaching Satoko to fire arms), Satoko shoots her in the abdomen and shoots three of her fingers off when Mion tried to make a grab for her gun. Mion suspects Satoko of lying to her and pulls out her gun going to shoot her when Satoko does not give her satisfactory answers.

She then leaves Keiichi locked up and goes to confront her. However, Satoko arrives on the house grounds carrying a bottle of soy sauce (claiming that she had received a letter from the Sonozakis to trade it with them). She traps him in a safe room after which she confesses to loving Keiichi and how he made her feel like a girl by giving her the doll. The police and Ooishi are tipped off about Rika's disappearance and pursue her to her house when she asked Keiichi to speak with her. After the deed was done, Mion hides her body in the septic tank of an outhouse and locks it to keep people from opening it. When Keiichi went to play with Satoko and the other kids, Mion seizes her and strangles her to death with her bare hands. At school, she quietly eavesdrops on a conversation Keiichi was having and suspects Rika of cursing Keiichi due to her being the shrine maiden for Oyashiro-sama. She then sneaks into her grandmother's room and shocks her in the throat with the taser.ДЄccidentally killing her grandmother, Mion then lures Chief Kimiyoshi to the Sonozaki residence to interrogate him even using the Nail Ripping torture device on him.

Because of Satoko's careful use of her words, Mion also became envious of her sister and wrongly comes to the conclusion that she was trying to take Keiichi from her.ДЄfter being horrified about what she had done, Mion vows to her slain sister that she would accomplish her goal of purging the village from evil by directing her rage towards the heads of the Three Families. Accusing her of putting Keiichi in danger of being demoned away by the curse, Mion accidentally strangles Shion to death when she was interrogating her. Enraged, Mion steals Shion's taser and uses it on her whilst attacking her. Growing suspicious because of the virus, Mion eavesdrops on her twin sister when she was speaking on the phone with Keiichi about being interrogated by Oishi. When she and the others attend the Cotton-Drifting Festival, Shion and Keiichi meet Tomitake and Miyo Takano and decide to infiltrate the storehouse. Unfortunately, Mion, who already harbored romantic feelings for Keiichi Maebara, further becomes obsessed with him once the illness was quickly advancing. Sometime after the competition, Keiichi wins a porcelain doll, and, after being talked out of giving it to Rena by Rika, he instead gives Mion the doll (Rika was hopeful that it would prevent Shion Sonozaki's rampage in one of the arcs of the original show). When the club go to play board games in a competition, Satoko silently injects Mion with L5 of the Hinamizawa Syndrome.

While conversing with Eua, Satoko mentions how Mion had never lost her sanity in any of the other loops becoming curious as to what she would do if she were under the influence of the Hinamizawa Syndrome. After she had inadvertently caused Rena Ryuuguu to go crazy culminating in Rika Furude committing suicide to escape the loop, Satoko Hojo accompanies her to the loop in which the Wataakashi-hen arc took place.

Amakusa shion