Shown throughout the series is the fact that Aiko is an android with an outdated computer and poor size memory. As the other three are based on storybook monsters its probable that Aiko is an updated version of Frankensteins Monster. ko is a common suffix for female names in Japanese and the quotaiquot may be derived from quotArtificial Intelligencequot. She performs housekeeping duties for the other girls because of her devoted mind. Her weight is 300kg or more and she hopes to get her own humantype body. Source:Wikipedia