You are Ms. Servant.

A maid suddenly appears at the house of high school student Hitoyoshi Yokoya, asking to be hired. However, her background as a former assassin makes Hitoyoshi think twice. From this fateful encounter, their lives together will forever be changed.

One day, Hitoyoshi is compelled to adopt a puppy that was left in front of his home. However, the maid has a childhood trauma involving dogs. Watching the two interact, the maid soon sees the world in a new light, even wishing to be "normal" herself.

Riko, Hitoyoshi's younger sister pays him a visit to see the puppy. Loving beautiful women, she easily got along with Yuki despite being an assassin. The maid’s skills awe Riko and decides to use Yuki as a subject for her independent research for school.

To experience a "normal" school life, Yuki enrolls into the same school as Hitoyoshi. Seeing boys rush off, she finds out the school store sells a rare yakisoba bread. Yuki heads out the window, leaving Hitoyoshi to worry whether she'd adapt well or not.

After the Nitta incident, Yuki decides to become Hitoyoshi's bodyguard, sticking to him 24/7. When she is distracted for a moment, a woman named Grace appears and takes Hitoyoshi hostage, seeking to kill Yuki for prestige and revealing her dark past.