I know in canon all of the CP9 Agents came from a special child soldier training island, but that's boring and doesn't even make sense for a good chunk of them??? (Kaku's too normal, Kumadori is too weird, etc, etc)
So here's a brief overview of my headcanons for their origins and specialties:
Rob Lucci - The Premiere Child Soldier, acquired age 9 after an act of extreme violence! He's a one-man-army who's meant to Send A Message (aka the assassinations that are very obviously on the WG's orders)
Jabra - An Ex-Bounty Hunter! A very disorganized one though, he did it mostly because he just likes killing people. He's good at short-term infiltration that ends in mass executions.
Kaku - Transferred from Marine Intelligence! Honestly Kaku is just a normal guy who is also very, very good at killing people! He's good at infiltration especially in urban environments and, unlike a lot of these guys, he can be trusted not to triple the death count on a whim!
Blueno - Also an Ex-Bounty Hunter! However, unlike Jabra, Blueno was a goddamn professional. He was probably a big name in his home sea before he dropped off the map. He, unsurprising, specializes in infiltration and acquisitions (His fruit is very helpful!)
Kalifa - Another child soldier! However, she got picked up at age 12, which means she has been socialized a little more. Similarly to Kaku she specializes in urban infiltration and, frankly, her relative weirdness is typically overlooked because she's a hot woman.
Kumadori - They just Found him, and frankly leaving him to his own devices seemed...unwise. Backstory sparknotes is that he was banished from Wano as a child with his assassin mother (she killed his father lol, he was an important lord and they had a domestic and well...) who taught him how to be Very Good at Murder. He specializes in no survivors OR in cases where the WG doesn't even want theories about their involvement, because he really doesn't act like a typical Cipher Pol Agent
Fukurou - Unsurprising another Child Soldier, acquired at age 8. Initially picked up for his power sensing ability, but then excelled in the CP9 training program. He CANNOT be trusted with infiltration missions and instead is usually sent on missions with the goal of no survivors. (This is why Fukurou is Jabra's favorite mission partner! He likes it when his targets know he's coming)
Nero - A child soldier, picked up at age 14! He had potential, but... Well let's just say Spandam was getting desperate to pad CP9's ranks after sending away 4 of his best guys for 5 whole years.
Donquixote Doflamingo - In my DonSwap!AU he ends up being dropped into the child soldier program at age 10 or 11. He, like Jabra, specializes in short-term infiltration that ends in mass executions! However, their methods are different enough that they hate working together
