The seven deadly sins:
Pride, Envy, Wrath, Sloth, Greed, Gluttony, Lust
the seven degenerated angels:
Lurifer, Azazel, Beelzubub, Beliel, Abadon, Mastema, Samael
Seven sins and seven punishments, go through the seven levels to wash away the capital sins and reach heaven on earth.
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Okay, I admit that the above is the official version of the introduction, purely for "deterrence"~
Seven Nights----Well, there are seven stories, and each story has a theme. Uh, please find the theme in the "Official Edition" introduction~
Sorry, suspended for some reason