A maid appears at the house of high school student Hitoyoshi Yokoya, asking to be hired; her background as a former assassin makes Hitoyoshi think twice.

Hitoyoshi is compelled to adopt a puppy that was left in front of his home; the maid has childhood trauma involving dogs.

Riko, Hitoyoshi's younger sister, pays him a visit to see the new puppy; she easily gets along with Yuki despite her being a former assassin.

To experience a normal school life, Yuki enrols at 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'll fit in or not.

Finding enjoyment in teasing the former assassin, Grace returns as a gym teacher; after much harassment, she clues in Hitoyoshi of the changes occurring to Yuki.