Amai Akuma Ga Warau

Amai Akuma Ga Warau (also known as 甘い悪魔が笑う or Sweet Devil Smile) is a 6 volume manga series by Authors Toriumi and Pedoro (Story & Art). It was published from 2010 to 2012 and was serialized by Nakayoshi.

Plot
Haruru Shirosaki, a girl whose father is a director, is always busy. Her best friend is Mami. She visits a girl's school across the road from a boy's school.

One day she sees a boy in the window of the boy's school. When she comes home from school the boy she had seen earlier is there saying he will become her butler? Is this just a dream?