For a very melodramatic shoujo originally from The Seventies, the animated version of Oniisama e... (from 1991) gives some REALLY creepy scenes.
Rei Asaka's apartment, which only has mirrors and Creepy Dolls aside of two/three furniture pieces. And this is without counting a certain spot in school, with the knife holes on the walls... Room Full of Crazy, indeed. Doubles as a Tear Jerker, considering the circumstances in which we find out about it.
Also, the scene in which Fukiko is swimming in a nearby pool and Nanako catches her. Fukiko invites her to take a dive, and it's even a little cute... and then she gets Nanako's feet stuck under a log and almost downs her. Of course she only intended to scare Nanako off, and gets her out in her arms when the poor girl is about to pass out, but it was still SO FUCKING CREEPY.
The kenzan deal is pretty scary in itself in the anime, due to the effective placement of the Pastel Chalked Freeze Frames and the borderline Psychological Horror handling. Nanako's picture above is her horrified reaction to it.
The scene where Rei, after being overloaded on drugs and with a high fever, mistakes Nanako for Fukiko and tries to kill her. And herself. Then turns into a Tear Jerker when Nanako barely manages to snap her out of it, and Rei collapses in tears.
While comparatively mild, after Nanako runs out of her birthday party, Mariko grows depressed and refuses to eat anything. Kaoru notices and tries to cheer her up, but Mariko angrily rejects her, saying "What good is health? Who cares about health!". The usually level-headed Kaoru becomes so infuriated that she lifts her into the air, shaking her and screaming into her face.
Rei was already making horrible, half-dead faces by the first episode. After Fukiko tosses an umbella at her and refuses to give her a ride, she takes some pílls and looks like a ghost while doing so.