As Shinpei and Ushio continue to watch Hizuru’s past interactions with Haine unfold, it’s clear Haine was not always evil incarnate, but more of a timid, frightened little girl Hizuru just couldn’t let be. Haine’s story of how the rest of her family starved is probably a big part of that; no doubt Hiruko inherited that story from the host body.
But the more Hizuru fed her, the more hungry Haine became, and she could no longer control herself. Hiruko’s instinctive drive to devour took over just as Ryuunosuke encountered a bloody Haine while looking for his twin sister. This is the day Ryuunosuke died, then in short order became a part of Hizuru.
Hizuru’s split personality wasn’t due to emotional trauma, it was an actual thing that happened as a result of Ryuunosuke’s copy bouncing off Haine (who is momentarily her former, innocent self) and imprinting onto Hizuru. Ryuu has powers similar to Ushio in the present, but by using them in his sisters body he puts immense strain on that body.
That said, he manages to kill two shadow babies and rescue Hizuru and a younger (but still old) Nezu. But Hizuru couldn’t do anything about the loss of her brother’s body, and her family soon moves off the island, much to Asako’s distress. As her boat departed, Hizuru spotted Haine wearing a patch where her right eye had been, promising the next time they meet she’ll kill her.
The memory ends abruptly, and Shinpei and Ushio end up back with Hizuru and Nezu about to confront Shiori. Ushio uses her memory transfer ability to bring the two up to speed, and they decide to regroup for now. Shinpei has Mio, Sou, Tokiko, and Tetsu meet him, Ushio, and Hizuru at the school, where he gives a speech about not wanting to run away, but to stand and fight…and for that he’ll need all their help.
Now knowing what awaits her by dutifully continuing her family’s practice of aiding Hiruko (betrayal and grisly death) even Tokiko agrees to help fight, leaving the cowardly holdout Tetsu no choice but to also agree. Nezu, keeping watch outside, ends up like Muldoon in Jurassic Park when he looks the wrong way at the wrong time and a “clever girl” kills him.
Just as Shinpei’s new plan is about to commence with everyone filled in and on board, there’s a flash and he loops back to when he was making sandwiches in the kitchen of his house. Clearly, one of Shiori, Shadow Mio or Shide (the four-armed one, embodiment of greed) killed him with Nezu’s sniper rifle. Shiori has realized that the starting points of Shinpei’s loops are getting later and later, so the faster she and her ilk make Shinpei die and loop, the faster he’ll run out of time.
That said, his starting point here is getting very late indeed with most of a second cour left; surely something in his favor has to happen soon. That is, unless, perhaps, reaching that point where there’s no time left is his natural next step on his journey…