Many things were born by chance, and Zack was no exception.
A puddle of leaked venom had flowed through a crack in an alchemical-tech facility into Zaun's sump district, pooling within an isolated pit deep below.
Zack gained consciousness in that environment and instinctively reacted to external stimuli.
An alchemical-tech conspiracy group noticed him and brought him back to their laboratory.
Through experiments, they discovered that this mass of gel possessed a certain psychological tendency. Simply put, it could imitate the type of stimulus it received. If treated with care and kindness, he responded with the joy and playfulness of a child.
But if pain and provocation were inflicted upon him, he fought back as well.
An Alchemical Baron named Takeda Saito wanted to research more weapons, but two researchers disagreed with him.
The two worked hard to counteract the violent teachings of the other team members. They wanted Zack to distinguish right from wrong, so they let him personally experience acts of self-sacrifice and selfless generosity.
Their efforts paid off. Zack did not become a brutal killing machine, but a gentle creature who regarded those two special researchers as family.
In the end, they took Zack and escaped from the laboratory when the opportunity arose. This naturally displeased Takeda, who ordered a manhunt for them. With nowhere left to go, they received Oran's protection, and Zack gained a new home as a result.
Although Zack's birth had been an accident, Oran was the one who understood his circumstances best.
The special nature of the Devil Fruit filled in that accident to a certain extent, ultimately creating this mercury Zack.
"Independent combat form."
The mercury gel detached from Oran's exoskeleton and condensed beside him into a humanoid creature.
Terminator, Venom, the Blacklight Virus, Mercury, the Chemtech Prowler—this new Zack was