*Disclaimer*
Just personal scratch.
Advised, possible spoilers.
Opinion & Informal

Art: 7/10
The anatomy and proportions of the human characters checked out. There were a few convincing scenes of nature shots. There were maybe one or two showcases of artistic skill. There were a few normal-looking wide shots. The environmentals and backgrounds looked a bit above average as they were a bit more filled and detailed. The impact shots were nice looking and did their job. The impact shot with the "Sorry for being a monster." looked creepy enough. The style was more realistic and leaned towards more real-to-life body proportions. Facial expressions were believable too but overall didn't feel too alive or impactful during moments of fear or anger. Overall, the art was good-looking and the shading and tones helped in setting the mood. There were one or two cases that could have been a bit better or used a bit more detail though.

Panel Progression: 5/10
The panel layout was about average. There were some tones that helped a lot in atmosphere building, but overall they didn't stand out too much as they were mostly used in select panels. The panel progression made sense and didn't create any confusing situations. The progression had a reasonable pace to most of the important bits such as the plot setup but it was a bit rushed regarding the entirety of the manga. There weren't too many uses of panel-cutting or anything that added flair to the visuals. Dialogue was at a nice volume; there wasn't too much or to little dialogue. Overall, the panel progression was just average as there was minimal flair elements in the layout or pacing.

Characters: 4/10
There characters were pretty lame and fit a lot of typical archetypes like the can-do-no-wrong nice guy, the innocent-beauty, etc. It was pretty telegraphed that the former two characters would be the ones to "survive." The character designs fit their personalities too which is fine I guess; I guessed that the nerd would somehow shockingly reveal a twisted personality. The character development was lacking because the characters were killed off as soon as everyone's baseline backstory was set up. Overall, none of the characters were interesting as their appearance basically dictated their personalities: The innocent-beauty with the sundress, the nerd in school-like clothing, the hostess in revealing clothing, etc. None of the characters had interesting development either. They just died off way too quickly.

Plot: 5/10
The plot setup was mysterious but honestly it was pretty easy to predict that a bunch of people would die and who would be the survivors. A more roundabout way of revealing the scenario would have been a bit more interesting. A remote and abandoned location, the way the invitation letter was worded, and the backstory to the visit screamed, "these people are going to die."

Development: 6/10
The development was mostly meh but I did like the twist. The twist was actually surprising to me. The twist regarding that idol girl was cool. The one part about the development I didn't like was that the characters who were being hunted down didn't have anything redeeming about them to feel bad for them. What I mean is that none of the characters changed at all from their middle-school days meaning that they ultimately didn't change for those 17 or so years. The bullies stayed terrible people for 17 whole years, seriously...The nerd pretty much only existed to explain the justification for their deaths. The nerd played no role other than to reveal some crucial information that would spell, "yeah these people are still bad, so don't feel bad for them when they die." People can change, but the characters didn't change AT ALL in 17 years leading up to their reunion. The nerd essentially existed to point this idea out. Everyone was so one-dimensional (especially over the course of 17 years) it's hard to feel any sympathy for their rushed deaths. This point is what I think made this manga fail in creating any sort of interesting survival aspects to the chases or their situation. The twist was the only good thing about the development in my opinion.

Conclusion: 5/10
Lame and left questions that should have been answered or not been made. The conclusion was pretty much that the two survivors actually died in the attack and that they were actually transported to Kiriko's world. The way this was executed was a bit confusing if taken as face value and I would have liked a bit more visual explanation or at least something that explained her world. How does she have her own world? Did that have something to do with how she materialized? Why did the nerd even want to send out the letters for someone he threw under the bus himself? How is it that the MC is able to interact with the people around him in Kiriko's world? I really wanted the how and why to the weird and unsupported twist ending.

Overall: 5/10
The reasons and explanations for a lot of the things in this manga were weak. The characters were weak too. The only nice things about this manga were the developmental twist around the end (not the twist conclusion) and the art. The monster wasn't really that scary or disturbing at all.