"Ichigeki Sacchu!! HoiHoi-san" is a manga series that blends science fiction, comedy, and action, centering around a unique premise involving combat androids designed to resemble young girls. The story is set in a near-future world where humanity faces a threat from an alien species known as the "Kiseichuu," parasitic creatures that invade and control human hosts. To combat this menace, a secret organization develops a series of highly advanced androids called "HoiHoi-san," modeled after schoolgirls to disguise their true nature as weapons.

The protagonist, HoiHoi-san, is one such android, designed specifically to exterminate the Kiseichuu. Despite her diminutive and unassuming appearance, she is equipped with an arsenal of advanced weaponry and combat capabilities. Her mission is to locate and eliminate the alien parasites while maintaining her cover as an ordinary schoolgirl. The narrative follows her interactions with humans, her battles against the Kiseichuu, and the challenges she faces in balancing her dual identity.

HoiHoi-san's creator, Professor Saionji, plays a significant role in the story, providing technical support and guidance. The series also features other characters, including fellow androids and human allies, who assist or complicate HoiHoi-san's mission. The tone of the manga oscillates between intense action sequences and comedic moments, often deriving humor from the absurdity of a schoolgirl android wielding massive weapons or the misunderstandings that arise from her attempts to blend into human society.

The plot progresses through episodic encounters with the Kiseichuu, each presenting new challenges and showcasing HoiHoi-san's evolving combat strategies. As the story unfolds, deeper themes emerge, such as the ethical implications of creating sentient androids for warfare and the blurred lines between humanity and artificial intelligence. The series maintains a balance between its lighthearted comedic elements and the darker undertones of its sci-fi premise, creating a narrative that is both entertaining and thought-provoking.