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Nightmare Fuel: Ar tonelico
Some the song are freaky scary
One of the Sublimation hymns, ee wassa sos yehar, consists mostly of a chorus literally snarling "Die!" in Japanese over and over again.
XaaaCi. That one starts off with Ominous Latin Chanting and heavy orchestrals, then slows down until it's just static, a One-Woman Wail, and a monotone voice quietly stating that she's going to kill you. Followed by a Scare Chord, more static, and a horrific metal screech that sounds like the crossing over of an Eldritch Abomination.
The setting itself is terrifying. Imagine living in a world with a war going on and one of the countries involved uses a weapon that damages the entire planet and causing what could be described as Doomsday. Fast forward to the second era where Elemia is at war with a Reyvateil who drops half of the Wings of Horus (the land FLOATING around the tower) into the Sea of Death, essentially killing millions of people. Let's not even get started with Metafalss and Sol Cluster's issues.