I was typing up my thoughts so far having mostly cleared the left side of the flowchart, but the topic purged while I was typing it :/ @Sad_Face Was gonna @Amazon_Shampoo but his username doesn't work for some reason :(
Alright so my thoughts so far (assuming So is definitely the cyclops killer, also a lot of this will prob be dumb):
So I haven't finished the first first path I went on, where the boss killed So. but given that he's the cyclops killer, she's either manipulating him or she suspected/discovered he was the killer and knowing the control he had over the police + investigation took matters into her own hands. TBH I think it's the former though.As for why she uploaded the video that incriminates herself, she knew it would be found by Date but I don't know why she would do this to herself though. As for the the original cyclops killers, the link to Iris and the Boss is clear. The original killer knows that So is the new killer due to his partnership with the yakuza. What is So's motive for the new killings? I think it's definitely related to Shoko's business dealings, but I'm not too sure how Renju got caught up in all of this despite his relationship with both Shoko and Iris. Could it potentially be that he was targeting victims "closer and closer" to Iris for a purpose? I was thinking if his final victim was to be Iris and all the killings up until then were to "get to her" or something, they skipped her mother so that can't be it. Maybe Iris wasn't the intended final target and maybe it's actually Hitomi. The original killers somnium seems to represent him + hitomi going about their daily lives, while someone (likely Rohan or Boss) being a constant presence/threat that kept growing.
For the Ota ending, I'm fairly certain he's cleared of any involvement in the conspiracy. Mayumis somnium doesn't seem to hold any greater meaning other than the obvious which is her memories of Ota. Ota wasn't in the car with Iris when she went to So's mansion. I believe Iris did kill So. How did she get past all the guards? She is involved with him.
Iris does have memories of the original cyclops killings, but they weren't very clear memories. Given what we know about her now I have a feeling they aren't suppressed memories. I have a feeling that the red girl in those memories might have been her mother? Especially considering that the original cyclops killer + Hitomi had a relationship. At least I hope that the red girl wasn't Iris because that would imply something very bad :/ The way that I interpret the version of her somnium with all the drawings is that she is very aware of the killings etc happening around her during her life and it's making her twisted (hence the creepy laughing). As for the version with the recordings of the murders, I think it implies that while she knows who's doing the murders maybe she wasn't involved herself and she is just "spectating" them. But her memory of Date killing someone was very clear so I feel like that part at least is very true.
As for Date, as he is now I don't think he's the type of guy that would murder people. But before he lost his memories he could have been a very different person. Given that Boss is involved with the original killings, and Date was in Iris's memories of one of the killings, I don't think it's a coincidence that Date ended up working with Boss after his memory loss and especially on this particular case. I don't think Date's somnium is particularly relevant to the overall conspiracy. It just represents IMO that the most important thing in his life right now is Mizuki and her well-being.
I have half a mind to say that Mizuki is uninvolved, but I'm not confident in that. She does have the first and therefore the likely most important somnium. It could be that Renju knew what was going to go down in the future and wanted her sent away. Her Somnium seems difficult to interpret. He is "in center of the storm" happening around her and she's trying to hide. Iris's body/corpse is below her and I have no clue what the implications of that are. Could it be something she desires?
Anyways, thinking is hard. Im gonna keep playing now