Hikari's mother passed away when he was ten years old. His father is in charge of on-site management at a newly built apartment building and does not come home much.

One day, Hikari's father introduces him to his new stepmother. She's fewer than ten years older than Hikari, so Hikari doesn't even call her "mom", he calls her "Kaori-san". She really wants to be called "Mama", so she does her best to take care of Hikari, but...

One evening, Papa was away as usual, and a television special about hypnosis was being aired. Hikari and his stepmother decide to give it a try, and he starts to feel unfamiliar emotions while playing naughty hypnosis pranks...