After the death of his mother, Taro Hanaukyo is sent to live with his grandfather, who he has never met. He soon discovers that his grandfather is gone, and has left the responsibilities of the house to him, and that included the hundreds of gorgeous maids ready to serve him 24 hours a day, seven days a week.

Taro's first day at his new school. He arrives in a helicopter and is miraculously successful in every thing he does.

Taro stays home from school and explores his new home. He finds courage and happiness while losing his shirt.

An ill-tempered member of a rival family introduces herself. She talks down to Taro and gets a double-helping of karma.

The head of the security returns. Taro quickly learns he's not the true Master of the estate.

Taro is getting suspicious of his luck in school.

A key emotional moment occurs between Taro and the head maid, Mariel, which relates to the "promise" of the title.

Within the Hanaukyo household, the "brain" is a supercomputer named MEMOL, which runs the mansion's entire system. The computer security department is overseen by Cynthia/Grace, making her the "brains" of the operation.

Taro finds himself alone in the mansion, forcing him to take care of himself. This provided him with an important opportunity for personal reflection and growth, away from the constant, overwhelming service of the maids.

The maids' overenthusiastic attempts to serve and pamper their new master often lead to chaotic, comical, or embarrassing situations for the shy Taro.

Taro is developing feelings for Mariel, the head maid, when he receives a shocking revelation.He is informed that he has an arranged marriage to Ryuka Jihioh, a member of a rival family. Ryuka is not pleased with the arrangement and is particularly annoyed to find that the new head of the rival family is a "whiny midget". To settle who is the better match for Taro, Ryuka challenges Mariel to a series of competitions.

Following the dramatic events of the previous episodes, a sense of tranquility returns to the Hanaukyo household.