There are 4 Requirements to this:
1) You must collect all the P Flonzer X Ship parts
2) Complete 40% of the X Dimension levels.
3) Unlock the Pirate Editor by passing a bill through Cam-Pain
4) At least the First two Stages of the main game complete
To get X-Dimension Maps you will need to buy them from a Cu-Sith in the item world. The are expensive to be prepared.
To Make things easier I will list the easiest way to Discipline enemies. You want Valvatorez, Fenrich and Valkyrie as you Allies in the Discipline Evil Symbol as these 3 Characters cover ALL weakness. Below is the following Discipline options to choose and who its effective on:
Tie Their Wrists (Default): Skull, Witch, Cleric, Sorcerer, Professor and Onmyo Monk.
Loyalty Training (Fenrich): Warrior, Valkyrie, Ninja, Lady Samurai, Beast Master, Masked Hero, Prism Ranger (DLC class), Kunoichi (DLC class), Medic (DLC class), Necromancer (DLC class), Winged Warrior, Slumber Cat, Prinny, Roc (Cocatrice), Mystic Beast and Death Saber (DLC class).
Forced Massage (Valvatorez): Flora Beast, Succubus and Felynn.
Unnecessary Favor (Valvatorez): Archer, Gunner, Armor Knight, Thief, Bouncer, Battle Suit, Android, Orc, Gargoyle, Dragon Zombie, Wood Golem, Dragon and Rifle Demon.
Go Travel (Valkyrie): Magic Knight, Celestial Host (DLC class), Sludge, Shroom, Spirit, Undead, and Death.
To get all the Ship parts you will need to Discipline certain enemies and have them lead you to treasure on any X Dimension map. This is best done on a new cycle as it resets all the levels and it gives you a bit of control over what maps get treasure since they only go to cleared stages. If you dont, you will just need to reload more often. You can obtain the 1st part in the list before the new cycle if you go that way. Just to make things clear there are 3 types of Flonzer X parts (G/U/P). I do not know if the other versions work but they can be obtained from the same Classes in the list below. I would just capture 3 of each so if you get the lower one you can keep it for the Ship part collecting achievement.
Here's the list: (X means its an X-Dimension)
9-6: Gambriel: Tier 2 Rifle Demon, lvl 446 Rear-Part
X-7-3: Thanatos, Tier 6 Death, over lvl 2500 Left-Side
X-7-6: Prinny King: Tier 5 Prinny, lvl 1390 Right-Side
X-10-1: Force Knight: Tier 5 Magic Knight, lvl 1540 Top
X-10-1: Alchemist, Tier 5 Professor, lvl 1540 Head
Now what you want to do is discipline them until the Treasure option is available. You get 6 tries and once they run you you need to complete 1 stage to refill your "actions". Once the option is available back out and DO NOT select the treasure yet! Save your game 1st as you will need to reload if you dont get an X dimension map, On a new cycle as long as you dont clear any normal stages, it should always go to any X Dimension stage that you cleared. So only clear the stages on this list. As you need to complete the normal stages to get the Gambriel on Stage 9. Do this before going to a new cycle if you choose to do it this way. I did this with all cleared normal stages so it took a bit of reloading to get the correct stage.
The Treasure is also set as soon as you get the map so retrying the stage will still net you the same Treasure. So do not save after getting the treasure map. If you dont get any Ship part, simply reload and get the map again from the prisoner. It also does not matter what X Dimension map the treasure appears on but you want one you can complete easily so dont worry if the treasure appears on a different X-dimension Stage. Another way to improve your chances at getting the right treasure is to increase the difficulty from the cheat shop. I put mine to 20/20 stars.
The Last piece of the ship is obtained by defeating the Meowkin Pirates in the item world. They are rare but you can make them more frequent via the cheat shop as well. They appear more often on the Treasure Routes as most other Pirates dont appear on those routes however you can find them taking the Item Growth Route as well. They also wont appear before Stage 21.
Once you have all the ship parts needed you can complete 40% of the X-Dimension maps which is 26/63 and then speak to the Professor at the bottom area of the base near the NPC that allows you to start a new Cycle.
If you have any questions, feel free to add them to the comments and I will answer them and add the info to this guide.
Thanks to JDuke705 for his recommendations/updates/fixes