As the series has gone on, Mimura's death has become one of my favorites in any story. It set the tone for the manga. One of the main characters, his face plastered all over everything, someone with their own sub plot going on to fight against the system, with two different ideas that could make it work, someone who practically everyone looks up to and wants to find and work with, who's good hearted, friendly, and characterized beautifully. And he happens to meet three people on his journey, Sato, Iijima, and Kazuo, one being his non main character friend, one being the unimportant non main character he kills by accident and one being the antagonist. Sato dies in his arms, and he runs for his life, using his bomb which would've absolutely blown up those in charge of the program to fight against Kazuo, yet he doesn't even kill him, effectively making his plan and everything he's done meaningless, only to die lying in his own blood with duct tape holding in his guts. Two volumes later we finally have Shuuya hear about this happening. Absolutely crushing reveal.
Seriously, the way they built up this character, not only to be respected and made incredibly human over time, but to be seen as a sigil of hope to most, and to have him die half way through the story accomplishing nothing seriously sets the tone amazingly. After this happens Shuuya, the main character before this, doesn't even appear(except for a panel where he is passed out) for two volumes. Anyone can die, the story will be unpredictable, and it will be gritty, horrible and nihilistic the whole way through, in a good way. And now we see the group which has been formed forever, with only few remaining in the game, who seemed to fully trust each other, kill each other due to delusions. Beautiful. Sorry Shuuya but your threat isn't only Kazuo..
Last note, I really liked Froggy's character. I think he illuminates the difference between this and other Battle Royale centered stories. Something like Kaiji speaks on humans in a broader scope and attempts to ask what is fundamental human nature. Battle Royale instead asks this question, WHAT causes people to act the way they do in a state of nature. In so it analyzes its entire cast and asks what their past was, what made them who they are, what their personality and their strengths and weaknesses are, and from that it answers why someone would act the way they do when put against a wall.
P.S. I personally love Kaiji, it's one of my favorite things ever, I'm just using these two stories to contrast each other since they tackle the same themes but in very different ways.