Mother Base Bonus Staff

In Metal Gear Solid V: The Phantom Pain, the player can unlock some bonus Mother Base staff, at most four in total (eight when separating them between genders), depending on how they pre-ordered the game. Each soldier is based on one of the four major military groups from the games (ie, FOX, FOXHOUND, the Militaires Sans Frontières, and Diamond Dogs). With the exception of Canine, these characters are currently exclusive to the Japanese releases.

Canine
Canine is a Diamond Dogs Mother Base bonus staff member who can be unlocked by doing pre-orders from any store outlet for the game in Japan, or by getting the Day One Edition of the Steam version in the overseas release. He or she is identified by their bright crimson hair and a Diamond Dogs tattoo on either their left cheek (should the recruit be male) or right (if the recruit was female). According to the Japanese PlayStation site, the two are named Crimson Canine and Garnet Canine, and also possess keen intelligence gathering skills and base building abilities.

Hound
Hound is a Diamond Dogs Mother Base bonus staff member who can be unlocked only by doing either an extensive Xbox One pre-order from Xbox Games or otherwise pre-ordering the game from the PlayStation Store during the booking period between July 23 and August 30. He or she is identified by their possessing green hair and a tattoo near their right eye, regardless of gender. The tattoo is based on the FOXHOUND logo, which is also implied by the name of the soldier. According to an advertisement for the pre-orders announcing them in a magazine scan, the male is named Viridian Hound, while the female is named Emerald Hound. In addition, they also possess high-level medical and intelligence gathering skills.

Fox
Fox is a Diamond Dogs Mother Base bonus staff member who can be unlocked only by doing a pre-order of the Day One edition of Metal Gear Solid V: Ground Zeroes and inputting the voucher code into The Phantom Pain when it is released. He or she is identified by light brown hair that almost comes across as blonde and, as their name implies, a tattoo near their left eye that matches that of the FOX unit emblem, regardless of gender.

Skull
Skull is a Diamond Dogs Mother Base bonus staff member who can be unlocked only by doing a pre-order of Metal Gear Solid V: Ground Zeroes via Game Tsutaya and inputting the voucher code into The Phantom Pain when it is released. He or she is identified by either a full set of white hair (if the recruit is female) or otherwise a shaved head (male) and regardless of gender, as their name suggests, possesses near their left eye a tattoo with the skull/pangaea portion of the logo for the Militaires Sans Frontières, Diamond Dogs' predecessor. However, their precise placement will vary, with the male having his tattoo be directly above the left eye, while the female has the tattoo right on the left eye.

Ground Zeroes unique characters
Completing a copy of Ground Zeroes purchased before the release of The Phantom Pain and inputting the resultant code into Konami CORE will allow the game's save file to be transferred over to The Phantom Pain, specifically any unique characters the player managed to retrieve. There are 19 unique characters total and the characters are as follows, with more information being found in their respective articles:
 * 12 standard enemy combatants
 * 4 in the Main Mission
 * 2 in Eliminate the Renegade Threat
 * 3 in Classified Intel Acquisition
 * 3 in Destroy the Anti-Air Emplacements
 * Prisoner 12282 (Destroy the Anti-Air Emplacements)
 * Escaped prisoner in the main mission
 * Glaz (Eliminate the Renegade Threat)
 * Palitz (Eliminate the Renegade Threat)
 * Hideo (Intel Operative Rescue)
 * Undercover JCS agent (Classified Intel Acquisition)
 * Bald Marine (Classified Intel Acquisition)

Note that all standard prisoners are found at Camp Omega, while the escaped prisoner and Prisoner 12282 is found in the refugee camp and the holding cell in the Admin Building, respectively. The 19 characters will also be unlocked by Main Mission 12.