Go to Chapter selection section, and head down to "more stuff".


All the way down to "credits".


Then go up to "see credits".


From where you start go to the left, and climb up the wall, then jump to the square thingy on the right.


From there continue to the right into the tunnel, then down again into a square thingy and right to the ledge over the end of the screen.


This part is a little tricky, try not to fall, otherwise you'll have to start all over again. There are some hidden paths as seen in the image.


Again a series of hidden paths. Be careful on the last part before the big jump, it's a bit tricky. After that go all the way up, until you see this:


And that's it, you've won the achievement, after that you get to play as Juni.