Non-playable characters (NPCs) include Admirals, Yonko, Shichibukai, “Super Rookies”, and many more. Like player characters, the capabilities of an NPC depend on their rank and tier, which is determined by milestones.
NPCs cost one fragment per two milestones. Fragment pooling is allowed unless stated otherwise.
Devil Fruit—varies
Position of power, e.g. Warlord—10 from one user
Each NPC starts with 3 ability slots. If the NPC meets the tier and rank requirements, these slots can be filled with an ability that costs one fragment (e.g. one cyborg enhancement, basic Rokushiki) or a type of haki. After the first three abilities, you will have to pay the full price of the ability to add it to the NPC's arsenal. For example,
NPC Bob is/has:
Tier 1, Rank 1 (2 milestones)—1 fragment
Tori Tori no Mi, Model: Peacock—3 fragments
Basic elemental martial style—free
Basic Rokushiki: Soru—free
Basic Rokushiki: Geppo—free
Electro—1 fragment
In total, the NPC Bob costs 5 fragments.
Purchased NPCs cannot have more milestones than your the mean milestones in your crew, with the exception of one.
Your crew can have one NPC who is stronger than your Crew Rank. For example, this can be the NPC commander of a marine crew. The highest number of milestones that NPC can have is:
Unnamed NPCs at Tier 0 Rank 0 are referred to as "grunts". They are free and do not require purchasing with fragments, but they serve as little more than fodder in the grand scheme of the story. These are the nameless and faceless marines and pirates who Luffy and Zoro send flying with no effort as a demonstration of their sheer power.
The number of grunts a crew is allowed to have is:
Member 1: 30 milestones
Member 2: 25 milestones
Member 3: 20 milestones
Member 4: 15 milestones
Member 5: 10 milestones
(30+25+20+15+10) x5 x10 = 5,000 grunts
Characters who can easily be brought into situations. These are characters who don’t hold a stagnant position in the world and can be brought into the beat of someone else's drum. One Piece is full of characters like these, and these NPCs should be the most freebase and fluctuate.
Characters whose personality, obligations, or whatever have you would keep them from joining up with players. These are most likely NPCs who hold higher positions or fame in the world, or are at the point where they are above a majority of the player base. These NPCs would be free to use, but they wouldn't hold permanent positions in any crew or group owned by players because they exist to be vehicles for story and character growth.
Recruitable NPCs can become non-recruitable and vice versa depending on how their situation changes as they're made use of in the player's story.
Characters so powerful or prominent that they couldn't be trusted in player hands and would need to get approved before-hand. These are your Yonko, Warlords, Admirals, Heavenly Dragons, etc. Players would be able to view their sheets to get an idea of information about them, but they cannot be used in roleplay for the purpose of storytelling without staff approval.