Kakushite! Makina San!!: 1x7

Thus, the Sisters Swap Places

Makina loses her body to her younger sister robot, Mimika. According to Makina, Mimika is an agent-type robot skilled at pretending to be fragile in order to manipulate others emotionally. To track down the now-missing Mimika, Eita proposes a strategy only a true mecha geek could devise.