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Nightmare Fuel: Magic Knight Rayearth
The monster of episode 8. It's Hikari, the cute fox Hikaru befriended. It reveals itself by bursting out of its skin, and its mouth is suddenly full of razor-sharp teeth.
Cephiro slowly decaying as the series goes on. At first the world is always in daylight and has beautiful scenery, but as time progresses earthquakes are more frequent, storms spring up, and it turns into Always Night.
The part in the anime where Nova disrupts the mystical process that Sierra is using to repair Hikaru's broken weapons and follows it via basically mind raping the half-conscious Hikaru for what feels like hours. Oh, and revealing that she is her Enemy Without.