This makes so many jumps it really is hard to take it seriously. Every time I try to stop Sora's death, the culprit retaliates? What? On the face of it, it seems understandable. But if you give even a thought to it, it reveals itself as stupid. Tokiwa was a completely unplanned, unrelated action that was never going to result in harm to Sora. Also, Hinata says that the murder must have been premeditated because a note was forged and the body was hidden inside the wall? That doesn't follow at all. The murderer could've done it without premeditation.
The real possible conclusion is not that this was all a premeditated murder laid out months in advance. The real possible conclusion is that the murderer also came back in time and is watching Hinata and the others.
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In addition, I wasn't going to say this before, but this chapter really makes it obvious. Can't harm the girl, Hase, with any life-disfiguring injuries. Can't tarnish beauty. Can only have the guy sustain long-lasting, debilitating injuries.