Fifteen years ago, an innocent fireworks accident caused by two boys, Ryunosuke and Takumi, destroyed an apartment building. One resident, Nomoto, lost his wife and child in the fire and suffered severe burns across his body. Fifteen years later, Ryunosuke tries to live a "normal" life while suppressing his guilt, whereas Takumi remains emotionally trapped in the past. When Nomoto suddenly reappears before them, the expected confrontation never comes. Instead, he shows an unsettling kindness—one that deeply disturbs Ryunosuke, yet offers a fragile sense of salvation to Takumi. As their paths cross once again in a reunion that should never have happened, the lives of these three individuals begin to shift in ways that will irrevocably alter their futures.

Seven men and women, consisting of three couples who are reluctant companions and one single man, play in the game with the secret that their relationship and friendship will collapse. Japanese remake of the Italian movie "Perfetti sconosciuti".

Set 15 years after "Twentieth Century Boys," Kanna (Airi Taira) reunites with several main characters from the first film in an attempt to stop Friend's increasing influence over the world and continued plans to eliminate humanity, as detailed in the New Book of Prophecy.