I dont know how to unlock it but once you you at the 2nd base,go down to the shower which is located at the bottom floor and press X.If Aya stays there,Be ready for the bath scene.

You can only see it on Episode 5 (the episode where Aya saw Hyde going into Babel). Before going on the mission, go downstairs and head into the bathroom. Check (press X) in front of the shower door.

You have to complete certain conditions per mission in order to have Aya take a bath in the shower rooms. I dont know what these conditions are because it's in Jap but after doing them you can now view the shower scene by pressing X in front of the showers. If you see text these dots "...." then just sit back and watch.

This scene is only viewable after you beat the game once in any mode. Further it is only available in episode 3 and episode 4 *the start of those chapters before you start the missions. Your armor must be in tatters, totally broken for Aya to take a shower. This scene will not be accessible on the movie viewer after you access it and beat the game. Which means you can only view it if you keep a save file at those chapters or just play the game again.

Way 1) The Scene is viewable before episode 2,3,4, and 5. As long as you complete feats from the last mission. If you don't know, Aya will say it if you try to view the scene.

Way 2) Rumored: It is said that if you beat the game 50 times then you unlock the scene to view permanently.

In addition to what siege said you must accomplish these things during the course of the main game, not during Case Training. I just wasted two hours trying to get the scene through training: No dice.

I was playing through on my first try, I nv did complete all the feats at episode 1 and 2 (completed some via case training) but i manage to complete all the feat in episode 3 (completed during the actual mission), before the start of chapter 4 i went down to the bathroom with a totally torn costume and the shower scene appeared. I kept a save file before that.