Jaco Checkbox is a character featured in hand in killer7, and the author of Jaco's Report. Although he does not feature in killer7 itself, he is implied in hik7 to have played a significant behind-the-scenes role in the game's plot and backstory. His real name is never revealed, as he prefers to go by the pseudonym 'Jaco'.
Like Holbert, Jaco is a FBI agent. He specialises in anti-terrorism operations, and as such becomes involved in combating the Heaven Smile threat when it first emerges in 2003. In September 2004 Smiles manage to infiltrate a bank in downtown Seattle which contained top-secret government documents, and Jaco is dispatched to oversee FBI attempts to wipe the creatures out. By the time the agency arrives one third of the bank's security staff, as well as one third of the building's regular visitors, have been transformed into Smiles. They begin to hunt down the remaining uninfected individuals and soon kill them all. Three teams of special forces are sent into the building, but they too are wiped out. In the chaos, Jaco decides to enter the bank alone and look for survivors; however, when he reaches the main vault he discovers his wife and daughter, who are already in the process of turning into Heaven Smiles. When they begin to laugh hysterically Jaco breaks down and shoots them with his rifle until it empties.
In the aftermath of his family's death, Jaco resolves to have his revenge on the Heaven Smiles. To this end he hacks into the FBI's most prized asset - a machine which can, given data of reliable veracity, predict the future with increasing levels of accuracy for every one of its predictions that comes true. This machine is known as Miss Jacob, and its use is restricted to the President himself. However, the sheer ubiquity of the Heaven Smile threat is such that even Miss Jacob cannot predict the near future with complete accuracy, lessening its usefulness somewhat in fighting the Smiles.
Despite this, following Jaco's incursion into the system, Miss Jacob manages to predict a hypothetical future where the Heaven Smiles' numbers are all but wiped out, leaving only one surviving Smile. Jaco discovers that in order to bring about this possibility, 49 consecutive predictions made by the machine must be realised, and only then will the final Smile appear. Jaco calls this figure the Last Smile, and, consumed by the desire for revenge on the Smiles, decides to personally ensure that the chain of predictions comes true.
It is revealed that the first link in the chain which leads to the Last Smile is the destruction of Japan. According to Miss Jacob, this event is known as "SUNSET". 200 Pulsar missiles will be launched from an unknown location in East Asia towards the country, but since the US will decline to deploy the Fireworks system Japan will be left to its fate. Tokyo, Fukuoka, Sapporo and Osaka - the four principal cities of Japan - shall be completely obliterated in a nuclear holocaust, effectively killing the country.
A short time later, Jaco sets out to track down and meet Andrei Ulmeyda, the enigmatic CEO of First Life, Inc. He utilises his old informants and contacts, and in doing so realises that their information tallies exactly with Miss Jacob's predictions. After learning that Ulmeyda acquired "something BIG" from Japan, he travels to InterCity in Texas and meets with the man himself. In his conversation with Andrei, Jaco implies that he knows the secret behind First Life's success - namely, Ulmeyda's possession of the Yakumo.
However, what he currently has is only a 'copy' of the original document; even so, the US government is extremely keen to get its hands on it and will stop at nothing to obtain it. Once this is accomplished, Jaco explains, they will no longer have a use for Ulmeyda and will dispose of him. First Life is simply a part of a wider simulation, carried out by the US government, of how to carry out the instructions detailed in the Yakumo. Jaco offers him a way out - if he can orchestrate the manner of his demise, he will defy their plans and at least be the master of his own death. Andrei agrees and proposes contacting the notorious group of assassins known as the killer7.
The next link in the chain of predictions, according to Miss Jacob, is the death of one Curtis Blackburn at the hands of the Smith Syndicate. While researching Curtis' activities, Jaco has several 'encounters' which assist him with his endeavours. The first is an anonymous phone call which he receives at his office; the man on the other end, whose true identity is masked by a voice scrambler, reveals Curtis' links to the Seattle Immigration Bureau and its role in his orphan smuggling ring. The caller explains how the orphans' organs are used to create Heaven Smiles, which are then apparently supplied to the US' main 'Opposition Party' (whether this is the Democratic party or the Republic party is left vague). However, the man predicts that Curtis and the Smiths will soon clash regardless of whether or not Jaco gets involved, and insinuates that he is being used as a pawn by somebody. After warning Jaco to lie low for the time being and not risk compromising his efforts to destroy the Smiles, the caller hangs up.
Jaco's second 'encounter' is with a young woman by the name of Samantha Sitbon, who introduces herself as a friend of his deceased daughter. After expressing her condolences and reminiscing about Jaco's daughter, she mentions that she is the caretaker of an elderly man named Harman Smith, who lives in a trailerhouse in southern Seattle with another man called Garcian Smith. Jaco leaps on this opportunity to get involved with the Smith Syndicate and bribes Samantha to help him out.
From this point on, Jaco uses Samantha as a part of his grand scheme in realising Miss Jacob's hypothetical future, referring to her as his 'alter ego'. Utilising his FBI training in hypnotism, Jaco uses his influence over Samantha to nudge the killer7 along the desired path and to act in accordance with his plans. However, around this time Jaco begins to suspect that Miss Jacob is actually an elaborate trick, and that everything has in fact already been pre-determined long ago.
In his research he learns that Curtis is deeply involved with a man known as the 'Governor of the EAST', who enlisted his services while Curtis was still working for the US government. He also learns more about the killer7's background, although details on the 'Bloody Heartland' incident (which in hik7 is said to have occurred in a small hotel in France, and not the Union Hotel in Philadelphia) are scarce.
Jaco learns that Harman was originally employed by the US government in his youth to carry out covert, behind-the-scenes investigations and assassinations. He was also contracted in the early 80s by a Japanese politician named Toru Fukushima (who in hik7 is a member of the Union 7) to carry out an important task at the Asian Security Protocol Meeting in Hakone, Japan; Fukushima used Harman to discover which way the participating countries would vote in a key decision, and then used his information to manipulate the eventual outcome of this decision. The details of how the partcipants voted is not revealed, but Jaco suggests that at this point the subsequent history of the world was somehow 'decided'.
In other words, the details of the agreement reached by the participants of the Asian Security Protocl set out (roughly) how events would occur for the next several decades; Miss Jacob simply reveals each step in this predetermined chains of events. Jaco accepts his role as a mere pawn in a much grander scheme whose true extent he cannot even begin to guess at - he is simply there to help the killer7 fulfil their function and somehow prevent Kun Lan's attempts to seize the 'undecided' future that will exist when the predetermined history laid out by the Protocol expires. The elderly FBI agent reveals that he uses Samantha to brainwash Harman into giving Garcian his instructions as decided by Jaco. A certain instruction or piece of information will eventually give Garcian his ultimate purpose: to exterminate the Heaven Smiles.
At some point in the future - implied to be around the time of Emir Parkreiner's showdown with Kenjiro Matsuoka on Battleship Island - Jaco decides to kill Kun Lan himself. According to his information, Kun Lan's 'real' self is actually a decrepid, elderly man who is kept under constant surveillance and heavy security in an underground cell somewhere outside Atlanta. Before departing to wreak his final revenge on the man responsible for his family's death, he leaves a last reminder for Emir, implying that he was ultimately controlling his actions from behind the scenes all this time: "Can you recognize who I am? This voice, do you remember it? The real me was always beside you."