When high school student Hitoyoshi meets his new maid, little does he know that the beautiful yet sullen woman has a dark history as an assassin.

A pure-hearted girl from the remote planet of Mercury enrolls into a school run by the corporation dominating the mobile suit industry.

When slovenly Amane falls ill after giving his angelic neighbor Mahiru his umbrella in a rainstorm, she steps up to care for him and his messy apartment.

The beautiful maid Lilith has recently been hired to care for the whims of her employer's son, Yuuri. However, Yuuri's overzealous skepticism of her every action keeps him on edge as he suspects devious mischief being plotted behind his back. Despite his paranoia, Lilith grows fond of Yuuri and often teases him as a way to further their bonding. The series revolves around the relationship between the cautious Yuuri and his wonderfully charming maid in this day-to-day oddball romantic comedy.