"Ichigeki Sacchū!! HoiHoi-san Legacy" is a short-form anime series that blends comedy, action, and science fiction. The narrative centers around HoiHoi-san, a small, maid-robot designed for combat against alien invaders. Created by a brilliant but eccentric scientist, HoiHoi-san is equipped with an array of advanced weaponry concealed within her unassuming, doll-like appearance. Her primary mission is to protect Earth from the relentless attacks of the Alien Empire, a group of extraterrestrial beings determined to conquer the planet.

The series unfolds through episodic encounters where HoiHoi-san confronts various alien threats. Each episode typically features a new alien adversary, showcasing HoiHoi-san's resourcefulness and combat prowess as she employs her hidden arsenal to neutralize the invaders. Despite her diminutive size and maid-themed design, she is a formidable force, often surprising both her enemies and the humans she encounters. The tone of the series is lighthearted, with a focus on humor derived from the contrast between HoiHoi-san's cute appearance and her deadly capabilities.

Supporting characters include the scientist who created HoiHoi-san, who occasionally provides background on her development and upgrades, as well as a few recurring human characters who interact with her during her missions. The Alien Empire serves as the primary antagonistic force, with its members ranging from comically inept to genuinely threatening, adding variety to the conflicts. The series maintains a brisk pace, with each episode delivering a self-contained story while contributing to the overarching theme of HoiHoi-san's ongoing battle to defend Earth.

The narrative emphasizes HoiHoi-san's dual nature as both a weapon and a symbol of humanity's ingenuity. Her interactions with humans and aliens alike often highlight themes of perseverance, creativity, and the unexpected ways in which technology can be used to protect and serve. The series balances its action-packed sequences with moments of humor and charm, making it an engaging watch for fans of quirky, fast-paced anime.