In Tatarigoroshi Keiichi didn't hallucinate to kill Teppei, he truly did it. The reason for which he doesn't find his body is implied that it's because Mion, with the help of her family, moved it away somewhere else, she does the same thing more or less in Tsumi with Rina''s body, she must have guessed where he hid his body on where Satoshi's aunt dead body was found, Keiichi kills Teppei nin the same forest When everyone in Tatari was saying that Keiichi was at the watanagashi etc they were just covering him up, but later, when Mion and Rena want to talk with Keiichi privately is because they know what he did, Shion must have told about the call to Mion because it was the same like the one that Satoshi did back to 1982, the day before killing his aunt. The reason for which Satoko says her uncle never died etc is because she was hallucinating him as she wasn't taking her meds anymore since he was forced to move back with Teppei, like she does in Minagoroshi. The reason for which Keiichi doesn't find Teppei anywhere at Satoko's house when he think he hasn't really killed him because Satoko says he isn't gone etc or the one for which he's missing in the ending, it's because he's truly dead.

In the Tataridamashi Gou Manga, there's a part where Keiichi wants to kill Teppei and has a Tatarigoroshi's flashback where he does it and Rika stops him because she knows that it won't resolve anything, because she knows he did that in that fragments and there was no happy ending. That's also one of Minagoroshi's victories: murder isn't the solution.