Oreko has quite a few: her following Sabitsuki around, if not otherwise occupied, when the diving helmet effect is equipped; the existence of the friendship meter; the implications that she made the machine effect to help with Sabitsuki's disease.
Child Oreko in the hospital room will wave goodbye to Sabitsuki when exiting if you have a high friendship meter.
It's hard to describe that bittersweet music that plays when Sabitsuki is asleep in her bed: it's very calm and emotional, and makes the game feel a lot deeper than the hellish nightmare simulator it's usually seen as at first glance.
When you hit Smile with the steel pipe, he laughs and gives a very, very creepy smile and pulls out his hammer. This only happens when he's with his little sister (and in a room in the school, but without the laugh). Then you realize: he's trying to protect the people he's close to.
The April Fools v0.16 update is part Mind Screw, part Nightmare Fuel, but it has a happy ending with Sabitsuki and Cleaner walking away together.
