First and foremost I'd like to get the praise out of the way. I love the character designs and the artwork with really cool panels and backgrounds. I'll never get tired of seeing the Mother-ship over Tokyo or the Title-drop displayed wackily across different buildings or in the sky.
The plot however is a complete mess of garbled nothings that I can't even. If the point of the manga was to be gibberish then it certainly succeeded however if it was MEANT to convey some greater message it feels like it got lost. Halfway through the manga it introduces every reader's dreaded 'Time-machine' but it works a tad different in that it effectively copies the User into a new timeline where it uploads your consciousness. This means that the old Timeline will continue to exist even if we jump to a newer one PoV-wise. Now initially Ooba states that it would delete the old consciousness but we learn with Ouran that this isn't true as both co-exist (which idk if this plot point even mattered).
Main point is that uploading your consciousness doesn't fix your own timeline and is pointless to upload to an alternative timeline as there's no guarantee that your knowledge would even be useful considering the differences as timelines aren't 1:1 copies. This is shown in the final arc (99-100) where there's like a Mandela Effect of things being named different as the smallest change and this timeline not having the Mother-ship or Invaders arrive at all to our knowledge. Did Koyama even do anything coming to this timeline? Despite him being the PoV for Chapters 90-99 it's like he's irrelevant except to revert the destruction of the 8/32 event. It's also possible it's a simulation of some kind through the pointing hands we see in Chapter 98 which we saw before in Chapter 82 + 89 (and earlier?).
A good portion of the manga is spent on a flashback (57-71) of the previous timeline which was entirely ridiculous and over the top. Kadode goes off the rails killing a bunch of different people and then feels guilty and winds up committing suicide, but it COULD have been really good if she was responsible for accidentally killing Kiho in this timeline or another character we knew of. Anyways on to the climax of the plot and my blehhhhh:
Ooba finds out the keyword to prevent 8/32 from occurring but coincidentally Kenichi ALSO shows up at the same time at the same part of the ship SOMEHOW. Literally how. This is like a Game of Thrones S8 moment with Jaime/Euron washing up on the beach together. Kenichi manages to appear whenever the plot needs him. Anyways we then get that shitty moment where Ooba by all accounts deserves to die, getting shot at by the military and then Kenichi who has absolutely murked EVERYONE up until now decides to shoot Ooba in the torso instead of the head (hurrrrrrrrrrrrrgh).
There's lots of deaths that happen throughout the series that to me miss the landing such as Miura committing suicide, Hiroshi driving to his death with the dog, that Reporter (Kate) who gets crushed by the Mother-ship debris. Plus tons of deaths from the 8/32 Incident which offscreen kills a lot of the cast. Characters who don't even get endings such as the Peace Cultists (Futaba subplot), Kenichi, Hikari, and Ouran/Kadode (who Tainuma suggests could still be alive in Timeline-2).
There's lots of repetition in the story. The intro of "If you can't grow courage..." happens a grand total of three times. Plenty of scenes of Invaders being slaughtered en mass. The Government covering up information. And that when the ship explodes Humanity will end. Over and over we're told these things for 90 Chapters. But Humanity doesn't end with 8/32 which feels like a huge waste. Also we're told that the A-Ray stuff is made up by the Government and doesn't exist but Ooba worries over it (55) and there's the time they mention Invaders giving off A-Rays at Ouran's apartment (37) which is practically confirmed since there's that Invader/Dog that's been following and are attacked (48/49).
Which perhaps this is meant to be a story bringing Humanity to the next stage of evolution. The Invader in Timeline-1 states that consciousness experiences the past/present/future/timelines all at once and the body alone processes time. This seems to be true because Koyama hears Kadode elsewhere in the ship (98) and Ouran/Kadode hear their own voices nearby (100). The Invader states it's not possible for Humanity to experience it because of gravity binding the body and mind too tightly, but then it doesn't really add up for the final chapter as though something is changing.
TL;DR:
My brain =