Sumeba Miyako no Cosmos-sou Suttoko Taisen Dokkoida (2003)

The Galaxy Federation Police (GFP) desperately wants to cover-up its personnel shortage with new mechanized power-suits. Suzuo, 19-years old, desperately needs a job. Tampopo needs an earthling to fit the prototype of her company's suit and declares Suzuo the perfect candidate! Strong competitors and the wacky A-class criminals fight against our hero in diapers, but they must not recognize each other out of costume or the test results will be a failure- but it's OK if they all live in the same apartment building to save money, right? (Source: Sentai Filmworks)