Very simple, all you need to do is press start, select the first title, any translation and make sure that you select voiced. Once you have done this just hold down the CTRL key, wait until you finish the prologue and continue throughout all the chapters. Pressing the SPACE key furiously will take approximately an hour longer.

Repeat exactly what you did the first time except select unvoiced. Also, you don't have to go and press CTRL through the whole story again, you can just easily select the last chapter (Chapter 08).

Now that you have finished both achievements for Narcissu 1st it is time to move on to 2nd. Select the second title, choose whatever translation and make sure that you select voiced, just like the first time. Now power through it again with CTRL.

Keep everything the same, select unvoiced and got through Chapter 19.

For some reason this achievement is hidden, but it only requires you to go to Epilogue & full credits. Make sure you have gotten all the other achievements before trying to get this one. Voicing does not matter.