If you read the notice on the clipboard next to the safe, you see that it needs five passcards to open it.

Which is a problem, because there are only four cards here. You need to find the fifth one, which is red.

You'll find it in Takae's room, Room 18, but only when she's not there.

Go into the room and look on the floor on the right, under where Takae normally sits. Aha!

Now for the safe itself. The notice on the clipboard is rather confusing, so I'll translate. The way the safe works is that you have to use the four cards to duplicate the pattern of colored squares you see on the screen now, only brighter. Read to the end of this hint for step-by-step directions on how to arrange the five cards to open the safe.

Slide a card, any card, into a slot, any slot, and let's see what we have to work with. The red card displays a row of red squares on the screen. Push the button above the slot to rotate the pattern clockwise; push the button below it to rotate the pattern counterclockwise.

Push the buttons until the red squares are lined up against the right side of the screen, as they are in the original pattern. Repeat the process with all five cards. But!

Even with all five cards rotated correctly, the safe doesn't open, and the screen doesn't look like it did. What's wrong here?

You may not have noticed, but every time you put another card in a slot, the colors you added overlaid any colors you put in before, changing them. That means you have to put the cards in the slots in a specific order to reproduce the pattern on the screen.

Pull all the cards out and let's look at the pattern more closely. It's not too hard to see that the red pattern, which is a single line of red squares, goes up against the right edge.

But the bottom square is very bright, the top square is dull, and one of the middle squares is green. So clearly, the green design goes on top of the red design --

-- which means the red card has to go in before the green card.

And since the purple design shows up completely with no other squares on top of it, it has to be the last card to go in. Get it?

If you don't get it, or if you do but you're tired of fiddling with the whole thing, here's the way to put in the cards to open the safe: