For this trophy, you need to use self destruct to remove 9S' pants.
First make sure self destruct is turned on by choosing System > Settings > Other > Self Destruct from the menu.
Then just press
and
simultaneously for 2 seconds and 9S will self destruct, removing his pants. Play in this state for 1 hour and the trophy will unlock. Transporting will repair self destruct damage, so be sure to repeat the self destruct if you end up repaired.