Aa Megami ni kokoro ubawarete? Aa Megamisama : Season 1 Episode 15

Skuld still can't accept sharing her sister Belldandy with anyone, let alone Keiichi. In an effort to prove herself more worthy than him, Skuld decides to build a labor-saving device that will serve and protect Belldandy from harm, the First Class Demon Mara, and especially from Keiichi! However, Skuld is a more skillful mechanical genius than she thought, and the labor-saving device begins reprogramming itself!