Is Reiko Sakakibara's aunt really her relative?
Reiko Mikami is the younger sister of Ritsuko Sakakibara (mother of Kouichi), so she really is his relative.


   She is the extra because she died once before, which pretty much proves she existed.


Another proof of her being Kouichi's aunt is


   Rei, the parrot she hates, was bought by her father after her death and was named after her.


You can also see her flashbacks from when she was a student in the manga.