An average loner-type, little sister who can't leave the house, an actress and her sister, the scientist classmate, and the idea that there's a syndrome that basically creates supernatural side-effects that alter reality around you. With two main characters who show such confidence while being almost completely monotone, and taking each other seriously despite deadpan humor.
I got the sense throughout the show that the main characters were more in the mindset of "Great. This crap again." rather than the typical anime-style "Aaah! Oh noes! (jiggle boob physics)". It set an interesting mood, wherein (at least as I saw it) the story could focus on what was happening, rather than the characters' reactions to it.
Complete with an invisible cease-to-exist character, memory loss, random causeless injuries, repeated day loops, a quantum physics clone... I had to marathon it. Didn't want to. Had to. Phenomenal. Might have to marathon it again. It's not often that most of the main characters usually show a deadpan flat expression, on both sides of the relationship.