So I've been thinking of the history of monoeyes in Japan. When did they get so popular. Was it something specific? I think one-eyed creatures have always been a part of Japanese mythology, and turning some into cute girls isn't a stretch, but I'm wondering if something started it in particular.
Here's a picture of Sabitsuki from the game .flow drawn by the creator, and one of the cosmetic 'effects' she has that changes her appearance, which is outright called Monoeye. The game is pretty old, from 2009, predating Nurse Hitomi and the '1st day of the month' trend. So it looks as if the idea of cute monoeye girls was around a while.