You will be given only partial access to Louis's Skyrunner once you've caught his eye with Joanna in tow and arrived at Port Brilehave. Knowing the only way to find a solution to break the Prince's curse is by stealing its formula, of course, the most important document is located deep inside this giant conveyance. In Metaphor ReFantazio, you have to find a way to break into Charadrius without raising suspicions. While most of this mission will be conducted in stealth, some battles are simply unavoidable.
When at the Metaphor ReFantazio in Charadrius, take a right into the hallway to Crew Quarters. Defeat two on-duty guards. Companion will suggest you speak with the soldiers present; from them, you learn that you need booze to bribe them. The forbidden place will be accessible when Strohl performs his spell.
Even though you are far stronger than those monsters, fighting them is simply not an option. This is the first stealth section you have to get through when you invade Charadrius. If he goes in as a group, that would raise suspicion, so our hero needs to take out guards from behind one by one. Gallical will give you the ability to see with increased eyesight.
There are three guards in this segment. Two of them remain stationary, and the third patrols. Take out the first by concealing yourself and taking the man from behind as he goes under the box. When that is done, climb the ladder up to the other area and take down the rest of the guards.
Collect Xanth's key card once you defeat all of the guards in the Charadrius' Crew Quarters. This is another unique high-ranking soldier, you only have three turns in which to destroy him. If you fail in doing so he will send a message to the ship, and re-direct you to the game over screen.
Most of the damage from Xanth comes from close-quarters combat; the surest method of defeating him is just putting him down with status illnesses. Since the Gunner Archetype has the Poison shot skill, I recommend carrying that. Your other option is to use Fire to potentially cause Burn.
A predicament will arise when you defeat Xanth in Charadrius. You can proceed further on either of two ways: Starboard and Port Corridor. Both areas will have miniboss enemies. It really is up to you; both options are pretty viable.
Ceiba patrols the Starboard Corridor, while Glechom is in the Port Corridor. Ceiba is resistant to all magical and physical damage. You'll have to employ the use of either the skill Heartbreak Strategem or the item Matterbreak Hammer in order to break his barrier and defeat him.
Should Glechom Daze, your party is able to be cured with Patra or Sulphurous Salt. Your best counter move against him will be to use the Knight's Proclamation talent on a single ally.
During my playthrough, I decided to engage Ceiba in Charadrius by using the Starboard Corridor. There are significantly more enemies here than there were in the previous area, and this area is also somewhat larger. Thankfully, your friend will give you a hand. What I'd do before heading down to dispose of the rest of the hostiles is take out all the guards on this upper level. Afterwards, come back to your friend so you both can take out the rest of the guards.
Once you defeat the second mini-boss under Charadrius, you have to obtain the last key card. The harder you try, Guard Chief Salva will get suspicious and would want to capture you with the help of Cabio. They are not strong at all, but you need to defeat them in three turns.
Helmsman Cabio can be killed quickly by using magic on him as he's weak against Lightning. Salva, on the other hand, is a much greater threat due to his AoE powerful magic casting skills. While Megido used back on him is the best option, you can kill him using Piercing Attack, like Poison Shot.
With the final key card, your team will instantly leave the Skyrunner. You will be entering Charadrius for the formula, but you'll be waiting until the Soiree to actually do so. Your bond will also deepen with Gallica upon completion of this dungeon to Rank 4.
Now that you know How To Infiltrate the Charadrius in Metaphor ReFantazio, you can apply it and continue enjoying the game.