RE: Mahou Shoujo Gundam. (Magical girl Gundam rp.)
Maybe something simple then? Like...
"In the distant future, humanity has set their sights on the galaxy beyond. They constructed a space station capable of emitting a wormhole intended to send humans beyond the reach of conventional travel methods. However, upon trying to use the wormhole relay, they discovered that it wasn't a way out of earth's influence... It was a way in! Kaiju, large monstrous beings, poured forth, and they were not friendly. The armies of humankind were not enough to drive back the threat, let alone close the portal. Thus, it was up to mankind's last hope; a squadron of specially-enhanced weapons known as... Mahou Gundams."
Insert anime opening here.
Of course, that'd be more Pacific Rim than gundam, but if we wanted to fight monster girls... XD