Infinite Undiscovery

For this achievement you must Vermify the nine characters with Lunaglyphs, other characters are not affected, these characters are:

Aya, Edward, Eugene, Komachi, Rico, Rucha, Balbagan, Vic, and Michelle.

You can only start to become vermified after you complete the story up to curing Edward of the vermification.

You must let each character fully vermify. To do this go to someplace with Lunar Rain (later in the game it falls almost everywhere, but a good place is the Cobasna Timberlands or right outside Port Zola). Now if you look at your character stats you will notice a small orb that will glow as you stand in the rain, after standing in the Lunar Rain long enough your characters will start to grow "wings" and get stat perks.

After this they will turn into black monsters and start attacking other characters, a little while longer the orb will turn into an eye, and the character will become translucent. This means they are Vermified and you must get all 9 characters into that state at one time or another.

Make sure and unequip the characters weapons and battle skills / disable magic for the characters you are vermifying so they don't take you out in the process.

Note: You DO NOT need to kill the vermified characters, just run into a nearby town and rest at an Inn (which is why its great near Port Zola).

You can also use these three items to increase the glyph and make your characters vermify faster:

-Lunar Incense
-Lunar Powder
-Lunar Fragment

Note #2: You will not be able to complete this achievement until Balbagan rejoins your party in the chapter Imposter, a little ways after destroying the Amber Chain.

There are 9 characters that must fully vermify:
Aya, Rico, Rucha, Edward, Eugene, Michelle, Komachi, Vic, Balbagan
Because Komachi is part of this list the earliest you can get this achievement is when you return to Kolton.
The area that I have observed most frequently gets Lunar Rain is just outside of Port Zala. Kill the two birds there and hide off to the side path that leads to Bihar Mines.
Take each character one at a time for this. You don't have to bother unequiping their weapons as there is a neat trick to this.
Once you have killed the two birds, sheath your sword and walk up the path to Bihar Mines so are out of sight behind the cliffs. Walk slowly and wait until your party member is directly behind you. Now turn around quickly. Your party member should have turned around and now be facing away from you in the direction you are looking. If not, try again until they are.
****Now put down your controller!****
Stand there in the Lunar Rain, and they will eventually turn black. Since they are facing away from you they don't know you are there and they won't find you because they don't move on their own. If you make the slightest motion, they find you and attack you (thus why I say put your controller down).
Once they turn clear (invisible), they have fully vermified. Run past them (which will scare them and the question mark will appear above them as they weren't aware you were behind them), run to Port Zala, rest at the inn (to get rid of the vermification effect) and switch party members. This takes about 45 minutes to do all 9, and is risk free if you use my trick.
[EDIT] It is possible for this to work with a full party (3 at a time)! Thus cutting your time required for this achievement to roughly 15 minutes! Just ensure that when you do the spin around portion of my trick that every character in your party is facing directly away from you. Wait until they all fully vermify and then run back to Port Zala.