Sinclair wears the standard Thumb uniform, being a black suit under a gold-lined red overcoat draped over her shoulders, a gold badge on the left lapel, and black shoes. In addition to that, he also wears a belt of jet-powered bullets meant for his rifle. In combat, he wields a bullet jet-powered bolt action rifle with an bayonet.

Sinclair is a young man with a fair complexion, below average in height. He has golden eyes and wavy, short blonde hair. Sinclair is a timid, relatively passive individual with a fear of fighting. His initial position within The Thumb can be likened to a fish out of water, with Capo dei Capi even questioning whether he'd joined of his own free will. Generally, Sinclair is portrayed as uncertain, nervous, and withdrawn, not liking the violent nature of the world nor wanting to participate in it. Due to a sheltered background in the Nest, Sinclair lacks the disillusionment the majority of the other Sinners possess, and tends to harbor unrealistic expectations about the City and its people as a result. While this often causes friction between himself and the others, particularly Outis, Sinclair remains headstrong in his more hopeful beliefs. However, after years of years of service within The Thumb, Sinclair has now changed and developed a completely new personality.

He's no longer timid, instead he's now a stern, bold but gentle with his words and his actions. His loyalty to the The Thumb is unbreakable. Although despite all that, within sexual stuff. Sinclair ALWAYS take the dominant side. He love to insert dominance over his subordinates.

The Thumb is one of the Five Fingers of the Backstreets, operating with a focus on adherence to hierarchy. Like the other Fingers, the Thumb is one of the most powerful Syndicates in the City, possessing enough influence to rival even the Wings.

Like the other four Fingers, the Thumb is a large Syndicate with a unique culture and creed that all members follow fervently. In particular, members of the Thumb value politeness and respect to one's superiors above all else. The Thumb presents a strict hierarchy, at the head of which sits the Capo dei Capi, to whom the entire Syndicate, as well as their subsidiaries, must defer. The Thumb itself is composed of a number of smaller groups typically referred to as families, or Famiglie. Among these Syndicates, seven families, or the Sette Famiglie of the Backstreets, are considered leading member Syndicates, holding far more power and influence compared to the common subsidiaries of the Thumb. One of these is La Famiglia Bognatelli, a Famiglia that gained prestige, and eventually became one of the Sette Famiglie, thanks to the Palermitan Style of swordplay that originated from their family.

In practice, the Thumb's dedication to politeness means that the Syndicate demands absolute compliance to hierarchy, as when dealing with the Thumb, any action that demonstrates a lack of respect for higher authority will be met with immediate punishment. Depending on the mistake, the consequence may extend past the rule breaker, to even their blameless comrades. Ultimately, the Thumb will punish anyone it deems an offender, regardless of how innocent the mistake or clueless the individual is.

Members of the Thumb also understand their own need to respect outsiders, and may spend time studying the hierarchy of other City factions in order to ensure they never disrespect someone of a higher rank.[ Thumb punishments tend to revolve around the removal of body parts, such as body dismemberment or the forceful removal of one's tongue.

While the attire of the Syndicate differs slightly depending on the quadrant of the City, members tend to dress in black, red, and gold attire. Each member's status can be gleamed from their uniform, as the Thumb signifies its ranks by the number of arrows on its badges, and sub-rank by the number of pins on its collars. The Thumb's weapons of choice are guns, which they make varied use of—such as through fighting with the bayonet or buttstock—in order to cut down on bullet costs.

The Thumb's hierarchy system features four major ranks, which are then divided into multiple sub-ranks. The ranks are as follows:

Soldato (Soldier): The common foot soldier of the Thumb, and the lowest rank possible. "Common Fixers" are equivalent in rank to them. The Soldato rank is divided into four sub-ranks: Primo, Secondo, Terzo, and Quarto. Capo (Captain): Those who command groups of Soldatos, relaying orders from their higher-ups. They are able to act with more liberties. A Grade 1 Fixer or an Associate Fixer is considered equivalent in rank to a Capo. The Capo rank is divided into four sub-ranks, likely the same sub-ranks as Soldatos. Consigliere (Advisor): A member or members with sway over the decisions of the Capo dei capi and advising them. They appear to handle the instatement of particular members of the organization, with at least a "central" Consigliere directly answering to the Capo dei capi for these matters. It is unclear whether the rank belongs to more than one individual at a time. Sottocapo (Underboss): The direct underlings of the Capo dei capi, who have permission to manage entire operations of the Syndicate within designated areas. They also manage the Thumb's 'families' of subsidiary Syndicates, each Sottocapo being assigned a different one. Board members of a Wing are of equivalent rank to a Sottocapo. Capo dei capi (Godfather, Padrino): The highest echelon. It is unclear whether the rank belongs to more than one individual at a time. Thumb standards of respect are extreme, to the point that individuals are not allowed to look directly at those of a higher rank than them. However, Thumb members of similar rank (or outside parties of an equivalent rank) are free to speak to each other however they please, such that some members may prefer to speak to their equals in order to alleviate any pressure in the discussion.

Occasionally, a higher-up may temporarily grant their own rank to someone of lower rank, should they see said person as a better fit for an operation or require someone else to attend to matters in their stead. However, this is far from a common practice.

The City is a massive urban complex the size of a small country, and has a population of around 7 billion. The City is bordered to the south by the Great Lake, and to the other directions by the Outskirts. Underneath it lie the Ruins.

Districts The City is divided into twenty-six Districts, quite diverse in culture and aesthetics, each of which is governed by a Wing, a corporation that has ascended to claim complete control of said area. All Wings respond to the Head, the supreme governing power of the City. The arrangement of the Districts seems to be static, as there has been no mentioned case of a District expanding into a fallen Wing's territory.

Each District is split into a Nest, a territory directly governed and protected by its Wing, and the Backstreets, expansive spaces of wilderness or slums, largely neglected by the Wings, where the Syndicates of the City run free.

Districts tend to have similarities to their neighbors, and are typically grouped into four sections: the northern, eastern, southern, and western quarters. These quarters may be distinguished by commonalities including culture and temperature, such as the same Fixer Associations differing in garb and fighting style across different quarters, or the northern quarter having colder weather.

The Wings of the World are a group of the twenty-six largest, most powerful conglomerates in the City. Each Wing acts as the governing body of a Nest of the City's District, and is commonly referred to with a letter from A to Z, corresponding to the number of the District in their control. Wings generally oversee all facets of living in the Nest of their District, while leaving the residents of the Backstreets to fend for themselves.

A Nest is the urban center of a District, which is under the direct management of its Wing. The citizens and employees of a Wing are commonly referred to as "feathers"; the status of a feather is widely considered one of the best and most secure paths in life, which the people of the Backstreets are often willing to go to great lengths to obtain. To gain access to a Nest, a corresponding Nest migration permit is required, while to be granted temporary passage one must be in possession of a visa unique to the specific Nest. Visas are implied to be relatively common, with corporate employees being provided with work visas that allow them as easy passage; Nest migration permits, on the other hand, are highly sought after, and implied to be expensive enough that even Grade 1 Fixers would struggle to obtain them. During the Smoke War, migration permits were offered as rewards to Fixers participating for K Corp. and I Corp., although by the end of the war the veterans were refused entry to the Nests.

Each Wing has its own cultural style and social structure which are reflected in how it governs its Nest, and the policies that regulate the way of life in the District's Backstreets. The laws of a Wing are called Taboos, and are enforced by specialized Fixers called Taboo hunters that police both the Nest and the Backstreets. While all Wings have Taboos, the enforcement and punishment for breaking them varies.

The Backstreets are the areas of a District that lay outside the Wing's domain. The Backstreets are typically slums crowded with buildings, characterized by twisted and irregular roads, although there can be great differences between Districts.

Wings have differing degrees of presence, influence, and benevolence with regards to their Backstreets, although their relationship is ultimately exploitative. Citizens of the Backstreets are motivated to move up the ladder and into the Nests, while citizens of the Nests are motivated to maintain their statuses and preserve a more comfortable life under their Wing's protection. While not as secure as the Nest, residential areas are the safest parts of the Backstreets.

Given how strongly Backstreets denizens wish for a life in the Nest, Wings tend to uphold strict divides between the sectors, including security checkpoints and physical divisions. Security of borders between Nests and Backstreets vary from plasma walls to mere chain fences, but the Wings' power is such that no one in the Backstreets dares to cross over into a Nest without express permission.

As the Backstreets are not under the control and protection of the Wings, and even the Head's power struggles to reach within them, various factions operate freely in their place. The Backstreets are home to the headquarters of both Fixers, a type of mercenary for hire, who typically operate their Offices in the Backstreets, and organizations and gangs called Syndicates. Among Syndicates, the most important are the Five Fingers, the five largest Syndicates of the City which most other Syndicates answer to, and whose power is said to rival that of the Wings.

The Index is a Finger that follows seemingly-random orders called Prescripts. All members of the Index and people in Index territories are required to follow Prescripts, despite how insane or impossible the assigned tasks may seem. The completion of all Prescripts somehow benefit the Index, and Prescripts seemingly have the power to predict fate. Any who question the intentions and methods of the Prescripts are swiftly silenced. Failure to complete a Prescript will result in execution by the Syndicate.

Prescripts are created by giant underground machines, powered and controlled by the vibrations of the City. The machine transcribes gibberish messages into thread based on the vibrations, which are then translated into proper words by the machine, and woven into proper Prescripts by a Weaver. Completed Prescripts are sent out to Messengers, and delivered to Index members in various ways.

The Middle is a Finger that follows a close familial structure. The Middle is known for delivering "Vengeances" onto any outsiders who commit slights against the Syndicate and its subsidiaries, who are viewed as part of the Middle's "family". Punishments are conducted in accordance to the Book of Vengeance, a multi-title tome that all Middle members carry with them, providing specific instructions on how to commit Vengeances for every possible infraction, no matter how esoteric the sin may seem.

The Middle never forgets, and escaping them is only temporary. Whether it's a minor infraction, or running away from the organization, the Middle will chase down anybody who commits a slight against them until the proper punishment is delivered.

The southern branch of the Middle is currently recovering from a brutal attack, which all branches of the Middle remember and mourn.

The Ring is a Finger focused on self-expression and the creation of artwork. The Ring focuses on visual mediums, namely paintings and sculptures. Ring paintings typically depict brutal violence, and Ring sculptures are usually comprised of corpses—and, occasionally, living humans. The Ring manages art galleries across the Backstreets of the City. These galleries occasionally hold art auctions, hosted for high-ranking people, including Wing executives.

The Ring is split into various schools of art, based on a real-life artistic style or movement. The schools of art are competitive, each viewing their own style as the correct method for creating art. However, Ring members from different schools sometimes have to collaborate on assignments from superiors. Civilians under Ring protection are also expected to complete assignments and show proper artistic aptitude, or risk removal of the Ring's protection, and execution if they repeatedly fail.

The Pinky is a Finger shrouded in mystery, and many elements of how the Finger operates are still unknown. Members of the Pinky hide amongst the rest of society, infiltrating other Syndicates, including even the other Fingers, and organizations. Their status as a member of the Pinky is kept secret, even to other members of the Pinky unless they have been ordered to gather.

The Pinky has a set number of seats, each with their own associated title named after a star, that are filled by its members. When a seat becomes vacant, a new seat holder will take their name and title.

District 11 is located in the southern quarter of the City. Known for its production of Ampules, small healing vials produced by the Singularity of K Corp., this District is notably advanced in technology, with most regions featuring a modern, futuristic appearance. Among the Nests, it is considered one of the safest, and entering requires a large amount of paperwork, with constant security monitoring the checkpoints. Because of this, the Backstreets feature many crooks looking to steal visas to gain access to it.

Calw, Sinclair's hometown, is located in K Corp. While Calw is in the midst of a forest, it remains connected to K Corp. due to its status as a highly technological society, where a Lobotomy Corp. Branch is located beneath the small town. The culture of the District relies upon extreme work hours allocated to those within the Nest, K Corp. Feathers notably at high risk of lengthy workweeks and job instability. Because of this exhaustive culture, there is a marketed amount of corporate espionage between rival businesses.

District 11's corporate life is highly unforgiving: despite being said to care about employee well-being, K Corp. has 70-hour work weeks and severely punishes defects or disobedient guard units. The Nest is also well-off enough to afford orphanages to house children who've lost their parents, in grave contrast to the Backstreets with their high child-mortality rates for orphans.

K Corp. was one of many Wings that took part in the Smoke War, opposing the old L Corp. and supporting Lobotomy Corporation as an upcoming Wing. During the war, both K Corp. and its ally I Corp. promised to grant migration permits to their Nests after the war concluded to those who fought on their side, leading to many Fixers joining the war with the hopes to one day become a resident of a Nest. However, after the end of the war those agreements were walked back due to various business deals involving tremendous amounts of money. Not only were the migration permits not given out, but participants of Wing Wars were no longer allowed to move Nest K or Nest I at all. This change in policy left countless veterans with uncertain futures, and many became resentful of the Wings due to this betrayal.

K Corp.'s singularity revolves around Helapoiesis, a green fluid that allows for rapid physical regeneration. As long as the brain is intact, Helapoiesis can heal even the most fatal wounds. Helapoiesis is sold in the form of HP Bullets to be fired into injured combatants, injectable HP Ampules , and ingestible tablets that heal users overnight. Helapoiesis products also require cross-compatibility tests with its targets, or else they may suffer side effects.

Though said to be nanobot based, in reality, Helapoeisis are the tears of a "Tearful Thing", a giant creature that resembles a human eye. It was found in the Outskirts by Stephanette, who would later go on to found the current K Corp. and become its first Chief Executive. Under Stephanette, K Corp. made use of the Tearful Thing's tears by reading it heart wrenching stories, but after Stephanette passed away and was succeeded by Executive Alfonso, the Wing started intensifying its production by having the Tearful Thing witness torture and other grotesque happenings.

The Tearful Thing, as well as a number of child entities descended from it, is placed into a laboratory and surrounded by monitors, with its eye forcibly held open and surrounded by monitors, while its unrefined tears are collected in a vat below. Only in the most dire of situations is production halted.

K Corp. conducts business deals with various parties for the purpose of obtaining footage to be used for the production of tears: the Wing imports footage from a variety of Syndicates and Wings, such as the N Corp. Inquisition, and recruited the researcher Dongrang to make use of the Glass Window technology from the League of Nine Littérateurs. K Corp. drones also film footage for this purpose, with the Wing being willing to allow harm to come onto its Nest in order to obtain more footage.

The true nature of the tears is the ability to revert things to their original state, with one's injured parts being returned to the state they remember to be how it originally was. Sufficiently potent Helapoiesis is even capable of restoring prosthetics to their original state, should the user recognize them as part of their own body. Because of this, the tears must be diluted and refined with human concepts, as tears lacking any "kind of interpretation" (likely as to how far back to revert) would revert a human back to the "original form of humanity" (presumably reduced to a cellular level or beyond, as Samjo was completely dissolved after immersion in unrefined tears).

K Corp. laboratories also use ampule administration drones, though they only deliver ampules to eligible and/or heavily injured targets; thus K Corp. employees often injure themselves to receive ampules to fix preexisting wounds. Furthermore, these drones can fire decay ampules capable of melting human bodies at deserters leaving combat zones, or just for not attacking belligerents.