My femshep fucked mai waiffu Liara in her underwear, so it's not a shock that she'd shower in her underwear as well.
The ultimate villain of the game is a macguffin artificial intelligence that culls the galaxy of all advanced organic life every fifty thousand years. It does this using advanced AI's known as Reapers (created from the memories of advanced races). Why does it do this you ask? I shit you not, it does it to prevent organics from creating advanced synthetics. The reason for this is that the synthetics created would wipe out all organic life (and not just most of it), which is clearly worse than a complete organic holocaust every fifty thousand years.
In addition, it jumps ahead thousands of years and doesn't show how any of the main characters made out after the events at the end of the game (except for a select few that land on a tropical planet somewhere. A select few including dead squad mates for some reason.) Then, if you've been a good boy and gotten a high score, you get one frame of Shepard (on the ground after battling the Reaper controller known as the "Catalyst" aboard a hovering space station/weapon that explodes) taking a deep breath.