Sumomo and Kotoko on a mission to return forgotten panties is the exact kind of stupid-funny premise that knows exactly what it is. The special exists purely to watch two chibi androids cause maximum chaos for the simplest possible reason. It's disposable, it's ridiculous, it commits fully to the bit.

Hideki Motosuwa heads out and leaves his wallet behind, so Chii grabs it and goes after him. That leaves Sumomo and Kotoko by themselves in the apartment. Before long Sumomo realizes that Chii has also left her panties at home, and the pair set off on an eventful trip to bring them to her. The special is a short comedy with ecchi and romance elements.