Hello

I'm hoping someone can help me name an anime series that I saw years ago.

The episode I watched involved a boy/young man in a robotic suit fighting another robot/monster/alien (not sure, sorry ) through a city but during the fight (for some reason) he swaps places with a girl and the robot suit also changes to a more female form.

I remember it being really cool and funny but I cannot for the life of me remember what it was called. I thought it start with an "H" or a "K" but I could find anything that matched it in the AA listings. I apologise for the very poor description of the show but I only saw the one episode and that was about 10 years ago. If anyone can help I'd really appreciate it.