"Hemera" by Chie Yoshii. In greek mythology Hemera (Ἡμέρα- day) was the goddess of daytime and one of the greek primordial deities. She is the personification of day and the daughter of Erebus, god of darkness, and Nyx, goddess of the night.
Rokurokubi are demons found in Japanese folklore. They look like normal human beings by day, but at night they gain the ability to stretch their necks to great lengths. They can also change their faces to those of terrifying oni to better scare mortals.