Glad to see another game from you! They are always very interesting, but this one was really great. The people who push the rating towards 3 clearly don't know what to look for in a visual novel.
*Spoilers below*
The story is complex and full of twists, some of the side characters were written so well that I quite started liking them. Honestly, in the very beginning, I expected Liam's vote to be something weird, but I saw his choice I was like - woah, the main hero's dead this soon? Even later, it was never obvious whether you should or should not trust him. And aside from the story, there were even few puzzles and interactive areas, so we could have a little break from reading every once a while. Kotaro's running animation was fluent, had even a jacket waving in the air (I dunno why I noticed it) and standing on a person's head while having emotional dialogues is definitely one of my favourite moments.
To the things that could be improved. (Eh, I'm sorry; this review is basically all reading... if you do not enjoy reading you might not like this review, but giving it a try won't hurt anybody ^^;;)
On purely technical matter, sometimes it was frustrating to continue through dialogues, because you had to press "S" several times to go to the next talk, not just once. Also, I'd make the down arrow key show the whole text at once, not just speed it up. Somebody might read faster, somebody might not want to read while the sound of the text showing up still plays. Just my opinion.
Also, not everybody might have heard the phrase "memento mori" to be able to complete the puzzle - and trying to assemble an English word won't work for them. I know it can be skipped and six notes aren't that hard to put together (although that makes 720 possible options), but it might be better if a sentence like "It seems like Latin to me" popped after two minutes or so. Again, my opinion.
There were also some typos, I've noted some of them down. I can send it to you via message - if you want - no need to clutter up the space here.
Story-wise, I could have some remarks.
I know you need the characters say the things they said in the order they said it, but I'd add a few lines here and then to make them look like upset, nervous, panicking or anyhow more emotional. They all just seem way too calm for the fact that they were all abducted, locked in an underground dungeon with scary masks and poison bracelets on their feet, one of them is already dead and they are forced to vote for their lives, or die in six hours.
As it seems to me, Simon is a calm character who won't panic, Liam got angry, fine. But the others?
Nana is clear; supposedly she had some time to calm down while she was awake (but she should pretend to worry more). Alice and Sera are said to be joking to lighten up the situation, but in a situation like this one, every joke would be much more convulsive, maybe cynical. Not many people would manage to fend off every worrying thought and joke in such a playful way. Maybe Alice could be one of them, but probably not Sera.
I know that by accepting the situation, the story gets pushed forward, but staying rather calm when one of your friends is suddenly dead and you read things like "if two people die, blue door opens", etc? At least one of such a large group should be "less calm" - it would be more realistic, make us delve deeper in the atmosphere and get to know the characters better (which might come in handy, seeing as you plan two sequels).
To post an example: (Alice) You are an asshole, Liam, you killed me. (Kotaro) Alice is acting weird again. - or a similar argument Kotaro had with Liam in Chapter 1.
Is that really that weird? Imagine that somebody caused you to die in two hours, although you thought you can trust him. What would you say (or more likely *do*) to such person?
A slight plot hole might be in Chapter 4. If I haven't missed it, Nana says that they made all that to make you feel scared to leap in time, that to experience all that was the only way to go, but why did she had to make it in the complex game-like way? She could just gather everybody and shoot them before Kotaro's eyes and it would probably produce the same effect. So why did those two put you through all the puzzles? Did they want to test your time-leaping abilities, or does Nana secretely hate you because she is the one living, while Aria is dead; or something yet different...? I admit, I might have missed it.
Ew, I apologise for this meaningless pile of words - I just enjoy good stories and yours was a very good one with a lot of interesting plot-twists, and I thought these observations might help you make it even better.
Yeah, and good luck with the sequels, I'm looking forward to them! ;)