Naota's life is confined to going to school and living with his father and grandfather. The usually tranquil life in Mabase is rudely interrupted by the arrival of Haruhara Haruko, who bursts on the scene by running Naota over with her Vespa scooter and hitting him on the head with a Rickenbacker 4003 bass guitar. Later, Naota is shocked to find Haruko working in his house as a live-in maid. Haruko's search for the alien being Atomsk puts her at odds with Medical Mechanica. At the same time, Naota is being watched by Commander Amarao. The Commander believes Haruko is in love with Atomsk and Medical Mechanica is out to conquer the galaxy. The fortuitous circumstances get Naota involved in a three-way battle between Haruko, Amarao and Medical Mechanica.
When Haruko runs over Naota with her scooter and brains him with a bass guitar, his world doesn’t just get turned upside down—it gets incredibly weird.
The series centers on the misadventures of 17-year-old Kana, a high school junior who spends her days hanging out with her besties, Mossan, Hijiri, and Pets. They live unremarkable lives, until the day a Mecha falls out of the sky, along with a strange woman named “Haruko.” Her plans for Kana and her friends involve the force known as “ATOMSK.” Kana will have to risk everything to decide whether or not to help… like she really has a choice!
Many years have passed since Naota and Haruhara Haruko shared their adventure together. Meanwhile, the war between the two entities known as Medical Mechanica and Fraternity rages across the galaxy. Enter Hidomi, a young teenaged girl who believes there is nothing amazing to expect from her average life, until one day when a new teacher named Haruko arrives at her school. Soon enough, Medical Mechanica is attacking her town and Hidomi discovers a secret within her that could save everyone, a secret that only Haruko can unlock. But why did Haruko return to Earth? What happened to her Rickenbacker 4001 she left with Naota? And where did the human-type robot "Canti" go?