Ichigeki Sacchuu!! Hoihoi-san: Legacy (2012)

In the year 20XX, insects have become immune to all pesticides. To combat the rising plague of cockroaches and other household pests, the tiny, doll-like extermination androids known as "Hoihoi-san" were created. They can hunt down insects and kill them with such miniaturized weapons as minuscule machine guns and tiny combat knives. They can also (and at the same time) be treated as dolls, by dressing them up in costumes and buying accessories for them. The main robot of the anime wears a maid uniform and rabbit ears as accessories.

Source: www.anisearch.com/anime/8005